Knee Pain and ICD-10 | Blog

Knee Pain and ICD-10

Knee Pain and ICD-10

Knee Pain is very difficult to discuss in a Blog because there are so many potential causes of knee pain, a very common Chief Complaint of Orthopedic patients. The basic, generic code for "Knee Joint Pain" is M25.56 _. This code "implies" that the cause of the pain is from within the knee joint, which it may or may not be. There are numerous causes of knee pain from within the joint, Intra-articular , such as disorders of articular cartilage, synovium, menisci, ligaments, arthritic conditions from various causes, to name a few. However, there are many disorders that cause knee pain that are outside of the joint, Extra-articular, such as tendinitis, bursitis, muscular disorders, and neuritic disorders. Knee pain can also be an element of Regional Pain from problems arising from other areas such as the hip, thigh, knee, and lower leg. Add to this is the fact that knee surgery is very common for treatment of these various things, but unfortunately, not all knee operations provide complete relief of the pain such that Postoperative Knee Pain as a residual can add to the coding dilemma. This brings into the picture the G89 and certain T Codes. In this Blog I am trying to confine the discussion primarily to those disorders that arise from the anatomic elements of the knee including the distal femur, patella, and proximal tibia and fibula for the bony elements, and the soft tissues, or non-bony elements, both inside and/or outside the joint.

In most of my Blogs relating to joint pain, I usually exclude acute traumatic disorders (S Codes), but many of these acute injury problems can arise in what would seemingly be rather minimal to mild, or otherwise innocuous trauma, such as a minor slip or twist that many patients might not give much attention to at the time, and go on about their business. These minimal events may result in some persistent pain problems for which they do seek help. In the elderly, these minor events may be an aggravation of an underlying problem which has only been a mild or intermittent nuisance in the past. Consequently, there is some discussion in this Blog of some of these possibilities.

In going through ICD-10 and researching information for this Blog, there are some areas that need some specific attention and discussion. One of these is Effusion versus Hydrarthrosis , and the other being the topic of Instability and/or Joint Laxity. The discussions of these are included in this particular Blog, but what is said about these topics can apply to any other mobile joint. This discussion is not unique to, nor isolated to the knee joint.

In trying to discuss Knee Joint Swelling , Effusion , or Hydrarthrosis , one aspect is determining whether the swelling is outside versus inside the joint. Swelling outside the joint is usually generalized and diffuse around the knee. There may or may not be excess fluid within the joint associated with this. When the swelling and fluid are within the joint, then we are talking about Effusion and/or Hydrarthrosis. For practical purposes, at least in the United States, Effusion and Hydrathrosis are pretty much considered to be the same thing. Technically, however, there is probably some difference. In general we consider an Effusion to be excess fluid formation/accumulation inside the joint due to some irritation or inflammation of the joint lining, the synovium. This irritation/inflammation can occur all by itself (synovitis), but is often secondary to some other intra-articular disorder (articular cartilage, meniscal, etc.). The term Hydrarthrosis is sometimes used in Orthopedics in the United States, but is not the most common term used for excess fluid within the joint. We are much more likely to say that the patient has a Knee Joint Effusion than to say that they have Hydrarthrosis of the knee. Both physicians and patients may refer to this as having "water on the knee." But, there is one "catch" to this concept of "water on the knee" which is that the Pre-patellar Bursa, between the skin and the patella, and outside of the joint, can become inflamed and fluid-filled, presenting as a fluid collection on the front of the knee. This can also be considered "water on the knee." Hydrarthrosis tends to be used for fluid in the joint which appears to have occurred "spontaneously" and without any other discernible cause or contributing disorder. It can occur as an isolated, one time event, or can occur on repeated occasions (called Intermittent Hydrarthrosis), and can affect only one joint, or could affect several jointsindependently or simultaneously. Therefore, the differences between Effusion and Hydrarthrosis are minimal and subtle. For the most part they are pretty much used interchangeably.

Another area to be discussed is that of Instability and joint Laxity. There are two aspects of this which make it confusing, the subjective sense or complaint of instability by the patient as a symptom versus the objective findings on examination of a true joint abnormality or ligamentous laxity that would support a diagnosis of "Instability." From the subjective side of this issue the patient feels that they cannot trust their knee to support them. They may say that it buckles, gives way, collapses, or they may say that they have a "trick knee." From the standpoint of the Orthopedic Surgeon, the problem is finding on examination some abnormality which would account for the patient's subjective complaints. This is not always as easy as it sounds. Most often we are looking for some previous injury or joint disorder that would account for true Joint Instability or Laxity, particularly ligamentous problems, old or new. Adding to some of this confusion is that some people by their very nature or constitution are "Loose Jointed." These are people who may say that they are "Double Jointed." These are patients whose ligamentous support of their joints is so loose/lax that they are capable of partially or completely dislocating their joint or joints, and can also with little or no effort reduce the joint back to its normal position. They may even demonstrate this as a "Party Trick" in social circumstances. These patients also have excessive range of motion of their joints when compared to what we would consider to be normal. These patients are often considered to have Hypermobile Joints and/or General Joint Laxity. The knee joint can be affected by any and/or all of these possibilities. Patients with complaints of "Instability" can certainly have pain associated with or as a result of it.

In considering how to organize the information for this Blog into some rational form, it is almost impossible. I am basically "stuck" with the organization and presentation of the coding information as presented by ICD-10, as "messy" as it is. Therefore, I will go through the Musculoskeletal Codes (M Codes) with pertinent discussion of each as it applies to the knee, some of the Congenital Malformations and Deformations of the Musculoskeletal System (Q Codes), then Injury Codes (S Codes) for what might be categorized as "Acute Knee Pain," and finally some G Codes, of which very few are going to be primary causes of knee pain, but can be used as an adjunct codes for knee pain from previous injury or surgery, or as primary codes as it might pertain to Pain Management.

M Codes: Disorders of the Musculoskeletal System:

For practical purposes, nearly all of the M Codes can cause knee pain.

Arthropathies of the Limb Joints (M00-M02):

  • M00: Infectious Arthropathies, i.e. Septic/Pyogenic Arthritis of the Knee:
    • These disorders certainly do occur, and as defined in ICD-10 can be either Direct, in which the causative agent, usually bacterial, is found in and can be cultured from the joint. It can also occur as an Indirect infection which has two types: Reactive, in which the knee joint infection is an aspect of a systemic infection (but neither organisms nor antigens can be found in the joint), or Post-infective, in which the microbial antigen of the infectious agent can be identified in the joint, but cultures are negative.
    • M00: Pyogenic Arthritis
      • M00.06 _: Staphylococcal, which is probably the most common,
      • M00.16 _: Pneumococcal, which is very rare,
      • M00.26 _: Streptococcal which is probably next most common after
        • Staphylococcal, and then there is
      • M00.86 _: "Other" bacteria.
      • These diagnoses need to be supported with a specific bacterial code from the A and B Codes. In the case of a Septic Knee Joint of the Direct Infection type other than those listed above (i.e. in Diseases Classified Elsewhere ), and that is a part of a Systemic Infectious Disease,
      • M01.X6 _ applies to the knee, plus a code for the general Systemic Infectious Disease.
    • M02: Post-Infectious and/or Reactive Infectious Arthropathy: The most common would be Reiter's:
      • M02.36 _ , followed by "Other" Reactive Arthritis: M02.86 _. These all require a 6th Character for laterality.

Inflammatory Polyarthritis (M05-M17):

  • These are disorders of a systemic nature that can include the knee as part of their process, but can also occur as isolated to the knee joint. The most common of these would be:

  • M05: Rheumatoid Arthritis with a positive (seropositive) Rheumatoid Factor:
    • M05.76 _ would be for Rheumatoid Arthritis of the knee without other organ or system involvement, and
    • MO5.86 _ would apply to "Other" Rheumatoid Arthritis with positive Rheumatoid Factor.
  • M06: "Other" Rheumatoid Arthritis:
    • M06.06 _ would be for RA of the knee without a positive (seronegative) Rheumatoid Factor ;
    • M06.26 _ for Rheumatoid Bursitis of the knee, which is not very common, and
    • M06.36_ for a Rheumatoid Nodule in the knee region, which is generally rare compared to other locations.
  • M08: Juvenile Rheumatoid Arthritis, of which there are several varieties, with or without positive Rheumatoid Factor, but all of which could cause knee joint pain. (5th Character 6 for the knee, and 6th Character for laterality, where applicable).

  • M1A. & M10.: Gout is included in the Inflammatory Polyarthropathies. Although this is generally considered to be a systemic problem, and most commonly heard of as involving the toes and ears, and as it applies to the presence or absence of tophi. It can certainly affect the knee joint as an isolated process or as a manifestation of systemic gout.

    • M1A: Chronic Gout applies to both Intra- and Extra-articular affectationsof Gout. The most likely are:
      • M1A.06 _ _ : Idiopathic Chronic Gout of the Knee , and would include Gouty Bursitis;
      • M1A.46 _ _: "Other" Secondary Gout of the Knee. These are 7 Character codes with the 6th Character being for laterality, and the 7th Character for the presence or absence of tophi (0: Without tophi, 1: With tophi).
    • M10: Acute Gout certainly can affect the Knee.
      • M10.06 _ would be for Idiopathic Gout , which includes both knee bursitis and joint involvement,
      • M10.46 _ would be for "Other" Secondary Gout of the knee.These are 6 Character codes, with the 6th Character being for laterality.
  • M11: Crystalline Arthropathies: All of which can affect the knee. The 5th Character is 6 for the knee, and the 6th Character is for laterality.

  • M12: "Other" Arthropathy: many of which can affect the knee as an isolated phenomenon or as a part of a systemic disorder. The most notable of these for the knee joint are:

    • M12.26 _: (Pigmented) Villonodular Synovitis: probably more common in the knee than any other joint.
    • M12.46 _: Intermittent Hydrarthrosis: (for which I refer to the previous discussion regarding excess knee joint fluid).
    • M12.56 _: Traumatic Arthropathy: The use of this code is questionable, and I would probably limit it to a Traumatic Effusion resulting from some vague or very nonspecific injury. This particular code has multiple Exclusion's including Current Injury and Post-traumatic Osteoarthritis of the knee (M17.2-M17.3).
  • M13: "Other" Arthritis: Which usually means "None of the above."

    • M13.16 _: Monoarthritis (NEC), is for isolated knee "arthritis." This would be a last ditch code to be used only when all other possibilities are excluded, i.e. there is no discernible "cause."
  • M17: Osteoarthritis of the Knee, which includes:

    • M17.0/1: Primary Osteoarthritis (Arthritis) (M17.0: Bilateral, and M17.1 _: Unilateral)
    • M17.2/3: Post - traumatic Osteoarthritis (M17.2: Bilateral, and M17.3 _: Unilateral)
    • M17.4/5: Other Secondary Osteoarthritis (M17.4: Bilateral, and M17.5 _: Unilateral).
    • The issues in these codes are what constitutes "Post-traumatic Osteoarthritis" and what is "Other" Secondary Arthritis? I would tend to use the Post-traumatic Osteoarthritis Code Set for arthritis resulting from some previous, identifiable joint injury which could be specifically identified as the underlying cause of the current arthritic condition. A previous tibial plateau fracture would be an example. As for "Other" Secondary Arthritis, it would be good to know what that previous "Other" disease/disorder was that resulted in the current arthritic condition, which would exclude trauma. A previous episode of septic arthritis would be an example for this. As I understand the coding rules for ICD-10, if that previous condition, traumatic or otherwise, is clearly identifiable, then it should probably be coded as well. In the case of a previous joint fracture, that might require coding it with a 7th Character of S, as the new/current problem (arthritis) is now a Sequela of the previous identifiable fracture. If that previous injury is not clearly identifiable or code-able, then the M17. code would probably have to "stand alone."

Other Joint Disorders (M21-M25): This includes many affectations of the knee:

  • M21: Other Acquired Deformities
    • M21.06 _ is for Valgus Deformity of the Knee (Knock Knee, GenuValgum)
    • M21.16 _ is for Varus Deformity of the Knee (Bowleg, Genu Varum).
    • Both of these are common knee deformities, but the question is whether either of them is painful in and of itself. However, they are often associated with Osteoarthritis of the knee, and its presence can certainly contribute to the progression of the arthritis over time. The question is "which is the chicken, and which is the egg?" (i.e. cause and effect relationship). That is, does the arthritis develop because of or secondary to the deformity, or does the arthritis develop on its own, but progresses at a faster rate secondary to the deformity. After 40 years in practice, I am still uncertain. This also makes an issue of whether the arthritis is Primary or Other/Secondary. In my years of practice, I tended to code the arthritis as primary osteoarthritis, and then add the deformity code as an adjunct, contributing/aggravating factor. Nobody has ever convinced me that the deformity should be the primary code, and the arthritis secondary. Also, to add to the confusion, since these are acquired deformities, they could be the result of a previous fracture involving the joint that healed with a malunion resulting in the excess valgus or varus. In this case, I would probably lean towards using the Post-traumatic Osteoarthritis of the knee code as primary and the deformity code as an adjunct, supplementary code. This again brings up the issue as discussed under Post-traumatic Osteoarthritis as to if there was a previous fracture resulting the varus or valgus deformity, then that fracture should probably also be coded with the 7th Character designating malunion (P, Q, R).
    • M21.26 _ is for Flexion Deformity of the knee; that is, a flexion contracture (inability to fully straighten/extend the knee), with or without a known cause. This can cause knee pain, and contribute to the development of painful knee joint arthritis. For the Knee Pain, I would use
    • M25.56 _ and supplement it with M21.26 _. In the case of arthritis, it would be "Other" Secondary, and the deformity code would be adjunct/supplemental.

  • M22: Disorders of the Patella: This Excludes acute dislocation. All of the codes for the disorders in this Code Set can cause knee pain, and if chronic can lead to Patellofemoral Arthritis , for which there is no specific code in ICD-10. This disorder would "appear" to be included in the M17 Code Set. My "interpretation" of the M17 Code Set is that it applies to Unicompartmental (medial, lateral, and anterior (Patellofemoral) compartments), Bicompartmental Femorotibial Joint Osteoarthritis, and Global/Tricompartmental Osteoarthritis. However, is it possible that as a Disorder of the Patella , "Isolated" Patellofemoral Joint Osteoarthritis or "isolated" Patellar Osteoarthritis can and/or should be coded separately? That is, if the Patellofemoral Arthritis is "isolated" to the Patellofemoral Joint/Compartment, and not a part of Tricomparmental/Global Osteoarthritis, can or should it be coded with its own coding? If so, it could be coded as M22.2 _: Patellofemoral Disorder (i.e. Arthritis). If the "Osteoarthritis" is isolated only to the Patella (which is generally rare in and of itself), then the code
  • M22.8 _: Other Disorders of the Patella (for Patellar Arthritis) could be used. Another option would be to use two codes: one of the M17 Codes (depending on the type of knee joint Osteoarthritis), and add a supplemental code, M22.2 _ to designate/ specify Patellofemoral Joint Osteoarthritis, or M22.8 _ for "isolated" Osteoarthritis of the Patella. I would tend to go with the latter In that the more codes the better. Let the insurance company figure it out. I doubt that either the CMS or the Insurance Industry can figure this dilemma out. M22.4 _ is for Chondromalacia of the Patella (only), and I would refer to the Blog on Coding Knee Joint Chondromalacia for more information/discussion.

  • M23: Internal Derangements of the Knee: These are for chronic problems, not acute injuries, and there are multiple Exclusions.
    • M23.0 _ _: Cystic Meniscus: These are infrequent in the grand scheme of meniscal disorders, but they do occur. Chronic meniscal cysts can extend through the joint "capsule" to become extra-articular, but are still "connected" to the intra-articular portion such that they are both inside and outside of the joint. They occur most commonly in the lateral meniscus and less commonly in the medial meniscus, but generally they are in the middle third of the meniscus, not the anterior or posterior horn, as would be implied by ICD-10. There are codes for cysts of the anterior and posterior horns of both the lateral and medial menisci, but these would be infrequently used. The most correct codes for a meniscal cyst in the middle third of the lateral meniscus would be M23.06 _ , and M23.03 _ for the middle third of the medial meniscus.
    • M23.2 _ _: Chronic Meniscal Derangements is for old, chronic tears or meniscal injuries (Bucket-Handle), and M23.3 _ _ is for 'Other" Chronic Meniscal Derangements. From an Orthopedic Surgeon's perspective, these are one in the same, and I am not sure why ICD-10 divides them into two separate sets. Not all old meniscal tears or injuries are of the bucket-handle type, but mostly are other types such as radial tears, flap tears, or "degenerative" tears. With this in mind, I would tend to use the M23.3 _ _ Code Set for coding chronic meniscal tears as it covers the full spectrum of chronic meniscal tears.
    • M23.4 _: Knee Loose Body: Loose bodies in the knee joint are relatively common and may be cartilaginous, osseous, or osteochondral. ICD-10 does not really differentiate between these possibilities, nor does it specify a size differential for Loose Bodies, but Procedural Coding is such that they have to be large enough to require some extra work, such as a larger or separate incision, to retrieve them from the joint. Many "cartilaginous" loose bodies are basically cartilaginous joint debris, are small, and are usually removed by the continuous flushing, irrigation, and vacuuming/suctioning of the joint during arthroscopy. With this in mind, I would not code separately for "Loose Body Removal" unless it was large enough to require some extra work as described. In a general sense, Loose Bodies have to come from some place within the joint, such that if there is an identifiable cause/site/source/lesion within the joint, then that disease or lesion should also be coded.
    • M23.5 _: Chronic Instability of the Knee: As presented in ICD-10, this Code Set is pretty vague, and would have very little use in practice. Furthermore, I am not sure how to differentiate it from M23.8X _: Other Internal Derangements of the Knee, which Includes "Laxity of the Ligament of the Knee," and "Snapping Knee." The Code Set M24.2 _ _: Disorder of the Ligaments (Chronic Instability Secondary to Old Ligamentous Injury, and Ligamentous Laxity NOS) is much more specific in this regard, and for the most part, any "Chronic Instability of the Knee" is going to be the result of an "Old Ligamentous Injury" and not anything else I can think of. A good history and physical examination would provide a specific diagnosis or lesion that would account for the knee instability. I refer you back to the earlier discussion of Instability and Laxity.
    • M23.6 _ : Other Spontaneous Disruption of the Knee Ligaments: For practical purposes, this Code Set has very little use in that truly "spontaneous" disruption of knee ligaments rarely occurs. I don't believe I have ever seen it.
    • M23.8X _: "Other" Internal Derangement of the Knee: This includes both "Ligamentous Laxity of the Knee," and "Snapping Knee." Again, I refer to the discussion of Instability and Laxity earlier in this Blog. About the only usefulness for this Code Set is that it is specific to the knee, but it is otherwise very non-specific, as opposed to General Joint Laxity or Hypermobile Joints , which do not have ICD-10 codes. The closest would be M35.7: Familial Ligamentous Laxity , which implies a generalized genetic disorder of joints, and is not specific to the knee. Unfortunately, in order to make this diagnosis, you would have to examine multiple family members to confirm that it is a familial disorder. In this day and age that is nearly impossible. A good history and physical examination should probably lead to a more specific diagnosis.

    • As for "Snapping Knee," most people have a "pop" or "snap" in their knee(s), particularly when they squat down and/or rise up. If it is an isolated phenomenon (sound) or physical finding, and not associated with any other symptoms such as locking, catching, buckling, etc. that occur at the same time, and if there is no other identifiable joint disorder to explain it, this code could probably be used. However, not all "snaps" and "pops" arise from inside the joint, but can arise from extra-articular sources such as tendons. Also, "snapping" has to be differentiated from "crepitus," which is a phenomenon that can be as mild as a sense of "rubbing" in the knee all the way to a palpable and/or audible "grinding," "crackling," or "crunching" from within the knee. Crepitation with audible manifestations is not the same as a "Snapping Knee." I would only recommend using this code for a situation when the patient is concerned about the "snap/pop," but has no other symptoms or objective findings to indicate a different cause for the "snap."

M24: Other Specified Joint Derangements: This Code Set Excludes current injuries, and it should be noted that M24.1: Loose Body in the Joint excludes the knee joint (M23.4 _).

  • M24.26 _: Disorder of the Ligaments, which includes Chronic Instability secondary to Old Ligamentous injury, and Ligamentous laxity NOS. This would apply to old ACL, PCL, MCL, LCL, Posteromedial, Posterolateral, Anteromedial, and Anterolateral ligamentous injuries and any combination thereof.
  • M24.36 _: Pathologic Dislocation of the Knee Joint: This Excludes congenital dislocation or displacement of the joint, and current injury. For whatever it is worth, this is very rare.
  • M24.46 _: Recurrent Dislocation or Subluxation of the Knee Joint: This Excludes recurrent dislocation of the patella (M22.0-M22.1). However, it is for recurrent dislocation of the knee, but only to the Femorotibial joint. Recurrent dislocation of the knee is very rare, but mild to moderate degrees of recurrent subluxation do occur, usually as a manifestation of chronic joint instability, plus or minus some joint arthritis.
  • M24.56 _: Contracture of the Knee Joint: It is important to emphasize that this is a Joint Contracture as this Code Set Excludes muscular contracture (M62.4), and contracture of a tendon or tendon sheath without contracture of the joint (M62.4). For the knee joint, the most common form is a flexion contracture, which is the inability to fully extend the knee, but the patient may be able to flex the knee well or almost fully. Isolated knee joint contractures without being secondary to musculotendinous contracture do occur, but is rarely primary, and is usually secondary to some other joint disorder such as arthritis. It can also occur after surgical procedures, particularly if the knee has to be immobilized in flexion for a prolonged period during healing.
  • M24.66 _: Ankylosis of the Knee Joint: This Excludes Stiffness of the Joint without ankylosis (M25.6). As it applies to the knee, Ankylosis of the joint means that there is nearly no motion in either flexion or extension, and that the joint is essentially "stuck" in one position. Like Contracture above, Ankylosis of the knee does occur, but is rarely a primary disorder, but usually secondary to some other disorder.
  • M24.86 _: Other Specified Knee Joint Derangements NEC: This Excludes(2) IT Band Syndrome (M76.3). This is a pretty vague and non-specific code set as to what would be included under this code set for the Knee, but as usual, "Other" applies to "none of the above" M24. Codes listed.

M25: Other Joint Disorder, not elsewhere classified : This particular group of codes contains many that are applicable to the knee joint as a source of pain.

  • M25.06 _: Hemarthrosis is blood within the knee joint. However this Excludes Current Injury, which then begs the question as to how or why the joint became filled with blood? Unfortunately, the vast majority of Hemarthroses are trauma related, even if the trauma seems to be rather minimal. "Traumatic Hemarthrosis" of the Knee or any other joint does not even have an ICD-10 diagnosis code. It is "Included" in the S83 Code Set: Dislocation and Sprain of the Knee Joint and Ligaments. However, a "Traumatic Hemarthrosis of the Knee Joint" is not really limited to these "S83 Injuries," but can arise from other types of trauma to the knee including fractures of the bony elements such as Osteochondral Fractures and others that are contained within the joint (Tibial Spine), that have an intra-articular extension from the patella, femoral condyle, and/or the tibial plateau, and other "Blunt Trauma" to the knee soft tissues that do not necessarily result in dislocations, sprains, or ligamentous injuries. Therefore, I would conclude that a "Traumatic Hemarthrosis" is considered to be an "included element" of the traumatic source diagnosis, and would not require or warrant a separate listing in the Diagnosis List or a separate diagnosis code. Hemarthroses are also common after knee surgery, which is itself a "traumatic" event, but surgical procedures do not come with S codes. Therefore, this code, M25.06 _ , would probably be a legitimate code for a Postoperative Hemarthrosis, if no other cause can be identified. It might be wise to supplement this with information regarding the surgical procedure done. Other possibilities for Hemarthrosis would be Bleeding and Clotting Disorders such as Hemophilia or patients on Anticoagulant medications, where "spontaneous" bleeding could occur.
  • M25.16 _: Fistula of the joint could apply to the knee. However, this phenomenon does not occur in isolation as a primary disorder, but is usually secondary to some other joint problem, mostly commonly infection.
  • M25.26 _: Flail Joint could apply to the knee. A "Flail Joint" is one that results from other diseases or disorders, usually neurological, with muscular paralysis such that the patient has no muscular control of the joint or extremity, and it moves freely (flops around) on its own. This code does not seem to exclude Charcot joint.
  • M25.46 _: Effusion of the Knee Joint : This Excludes Intermittent Hydrarthrosis (M12.4) and Infective Synovitis, which for the knee would be Septic or Pyogenic Arthritis (M0 _. _ Codes) as already discussed. I would refer you back to the discussion of Effusion and Hydrarthrosis earlier in this Blog.
  • M25.56 _ : Pain in the Knee Joint : This is fairly self-explanatory and has been discussed in the early part of this Blog. This is not a definitive diagnosis code, but one describing a symptom or complaint. Once a pain causing disorder or diagnosis is made that would explain the patient's pain, then this code should be removed from the list. If there is no discernible reason for the patient's pain, then you could use this as a "stand alone" code. I would also refer you to the Blog related to Coding Pain.
  • M25.66 _: Stiffness of the Knee Joint, Not Elsewhere Classified : This Excludes Ankylosis and Contracture of the knee joint as previously described. Again, like joint pain, this is a subjective complaint (symptom) by the patient, that may or may not be supported by objective physical findings. The term "Stiffness" implies some limitation of joint motion. Often patients with knee problems will complain of "Stiffness" or "Tightness" in their knee, particularly in the morning when they first get up, or after a period of rest or inactivity when they get up to move and ambulate. Although it may not resolve completely with activity, it usually does subside some. While at rest, the joint may actually "stiffen," but I think this mostly reflects what muscles, tendons, and other periarticular soft tissues do when allowed to rest in one position.
  • M25.76 _ : Osteophyte of the Knee : Osteophytes, frequently referred to as "Spurs", are common around the knee, particularly with arthritic conditions. They seem to develop as a reaction to chronic inflammation of the tissues of the joint and bone. The explanation that I have used regarding these is that they are "Mother Nature's" way of the bone trying to "heal" in the presence of, or in response to surrounding joint deterioration and inflammation. If an osteophyte is large enough or in the right location in the joint, it can be a source of pain and tenderness.

Systemic Connective Tissue Disorders (M30-M36):

This category Includes Systemic Autoimmune and Collagen-Vascular Diseases . These are systemic disorders which can have joint involvement and manifestations, of which the knee joint could be one. Of the various ones listed in this group, Polyarteritis Nodosa (M30) , and Systemic Lupus Erythematous (SLE) (M32) are probably the most common. Of note is the code M35.7: Hypermobility Syndrome, or Familial Ligamentous Laxity. As previously discussed, this is a generalized genetic joint disorder, but because of the "inherent" ligamentous laxity of the knee, it could be the cause of secondary joint problems resulting in pain. In the M36 Code Set there are codes for Arthropathy from Neoplastic Disease (M36.1), Hemophilic Arthropathy (M36.2), Arthropathy of "Other" Blood Disorders (M36.3). Conceivably, any or all of these could cause knee pain. They all have a Code first coding note to Code also the underlying causative disorder.

Soft Tissue Disorders (M60-79):

The muscles of the thigh (quadriceps and/or hamstrings) could have a muscular disorder causing knee pain including:

  • M60: Myositis (infectious, non-infectious, foreign body granuloma, and "Other").
  • M61: Calcification and/or Ossification of the Muscles which could cause knee pain if the calcification or ossification is quite near or adjacent to the joint. The most likely cause of these would be the residual of:
    • M61.06 _: Traumatic Myositis Ossificans
    • M61.46 _: Other Calcification of Muscle
    • M61.56 _: Other Ossification of Muscle
    • In these situations, I would tend to code this as Knee Joint Pain (M52.56 _) due to or secondary to these disorders.
  • M62.16 _: Atraumatic Rupture of Muscle (Quadriceps) is sometimes seen in Chronic Renal Failure patients. However, more often than not, when these patient's "rupture their quadriceps," the actual rupture occurs in the quadriceps tendon at its insertion to the patella rather than up in the muscle itself. Therefore, a Quadriceps Rupture is more of a "Spontaneous" or "Atraumatic Tendon Rupture" than a muscular rupture.
  • M62.46 _: Contracture of muscle and/or tendon (sheath) of the Quadriceps or Hamstrings could result in knee pain. This has to be differentiated from Contracture of the Joint (M24.56 _) as previously discussed.
  • M62.838: Other Muscle Spasm or Cramp, primarily of the Quadriceps, could be used for knee pain associated with the muscle spasm. Again, I would probably code the Knee Joint Pain as M52.56 _ secondary to or associated with the muscle spasm/cramp.

Disorders of Synovium and Tendon (M65-M67):

  • M65: Synovitis and Tenosynovitis around the Knee Joint: This Excludes current injury and use, overuse, and pressure (Occupational) disorders. I would tend to limit the use of some these mainly to extra-articular disorders as opposed to intra-articular disorders of the knee.
    • Infectious processes outside of the knee joint include:
      • M65.06 _: Abscess of the tendon sheath
      • M65.16 _: Other infective Synovitis or Tenosynovitis.
    • Non-Infectious causes include:
      • M65.26 _: Calcific Tendinitis of the knee would be a possible source of knee pain, although this is not really very common.
      • M65.86 _: "Other" Synovitis or Tenosynovitis is too vague and nonspecific when compared to the Code Set M76: Enthesopathies of the lower limb, which will be discussed later in this Blog. I would recommend using an M76 Code as I think it is far more specific.
  • M66: Spontaneous Rupture of Synovium or Tendon : This does have specific application to the knee region including:
    • M66.0 _: Rupture of Popliteal Cyst
    • M66.25 _: Spontaneous Rupture of Extensor Tendon (within the tendon or at the musculotendinous junction) are also pertinent to the knee. I think this code would pertain to both ruptures of the quadriceps and the patellar tendons as both of these are a component of the quadriceps/knee extensor mechanism. As previously discussed, these are seen in patients with Chronic Renal Failure, though ruptures of the quadriceps are far more common than ruptures of the patellar tendon. I would also refer you to the Blog on Tendon Ruptures.
    • M66.35 _: Spontaneous Rupture of Flexor Tendon would apply to the hamstrings, but "spontaneous" ruptures of these tendons are very rare. These are usually traumatic in origin, and usually are in the muscle.
  • M67: Other Disorders of Synovium and Tendons :
    • M67.26 _: Chronic Synovial Hypertrophy, NEC , of the Knee could include intra-articular disease if there is no other identifiable and code-able disease that would account for the chronic synovial inflammation. When the joint synovium becomes chronically inflamed, it will sometimes grow excessively to become hypertrophic. There is usually an associated effusion. Usually, however, there is an identifiable disease disorder which leads to this chronic synovitis situation that should also be coded. However, I do not think that this code is restricted to chronic intra-articular synovitis, but could also apply to chronic extra-articular tenosynovitis of the tendons outside the joint. In other words, this code could be used for both intra-and extra-articular disorders of this nature.
    • M67.36 _: Transient/Toxic Synovitis would apply to inflammation of the knee joint as a manifestation of some febrile (possibly infectious) illness, but without there being a direct infection of the joint.
    • M67.46 _: Ganglion (of Joint or Tendon Sheath) has applications to the knee. But, this Code Set Excludes bursal and synovial cysts (M71.2-M71.3). Intra-articular ganglions do occur in the knee joint, are usually small, and are usually identified on MRI studies. These can be symptomatic. Extra-articular ganglions around the knee also occur, and are not the same as Meniscal Cysts.
    • M67.5 _: Plica Syndrome of the Knee is another cause of knee pain. "Plica" means a "fold" in the lining of the joint synovium. In the knee joint, these "folds" are the residuals of the embryological and fetal development of the knee joint. These can sometimes be large, thick, and tight, causing pain when they rub or get pinched during joint motion.
    • M67.86 _ is applied to "Other" Specified Disorders of Synovium and/or Tendon. This Code Set strikes me as being very vague and nonspecific, such that I would not recommend using it unless absolutely necessary. (The 6th Character for this Code Set is 1: Right knee synovium, 2: Left knee synovium, 4: Right knee tendon, and 5: Left knee tendon.) I would probably use M67.26 _ as discussed above.

Other Soft - Tissue Disorders (M70-M79):

  • M70: Soft Tissue Disorders secondary to use, overuse, and pressure (Occupational Soft Tissue Disorders), including:
    • M70.4 _: Prepatellar Bursitis, and
    • M70.5 _: Other Knee Bursitis, in which I would include Tibial Tubercle Bursitis.
      • Both of these disorders can be seen in people who do a lot of kneeling and crawling in their work such as carpet layers, tile floor layers, etc.
  • M71: Other Bursopathies: This Excludes the M70 disorders already discussed.
    • M71.06 _: Abscess of (Prepatellar) Bursa of the Knee
    • M71.16 _: Other Infectious Bursitis of the Knee, which would include bursal cellulitis without abscess of a knee bursa.
    • M71.2 _: Popliteal Cyst/Baker's Cyst without rupture (5th Character for Laterality)
    • M71.36 _: "Other" Bursal/Synovial Cyst of the Knee: There are other bursa and synovial cysts in and around the knee other than Popliteal/Baker's Cyst and the Prepatellar Bursa, and are different from meniscal cysts with extra-articular extension as has been previously discussed with meniscal cysts.
  • M76: Enthesopathies of the Lower Limb, excluding the foot. Enthesopathies are by definition disorders of muscles, tendons, and ligamentous tissues where they attach to bone, i.e. at the origin or insertion. Those listed in ICD-10 in the M76 and M77 Code Sets are only some of the "Soft Tissue Disorders" that could fulfill this definition. There are many other musculotendonous disorders that would probably be considered Enthesopathies, but are put in other Code Sets. This Code Set includes several pertinent to the knee: (5th Character for Laterality)
    • M76.3 _: IT Band Syndrome: This is pain on the lateral side of the knee over the lateral femoral condyle. This is caused by the IT (Iliotibial) Band moving back and forth over the lateral femoral condyle during knee motion, and is common in runners. In addition to local tenderness and possibly some swelling, there may be some soft tissue rubbing or crepitation felt during motion.
    • M76.4 _: Tibial Collateral Bursitis: ICD-10 includes in this Pellegrini-Stieda Syndrome/Disorder, but not Pes Anserine Tendinitis/ Bursitis. The Stieda-Pellegrini Syndrome or Disorder is for the most part a radiographic diagnosis in which calcification and/or ossification is found in the proximal aspect of the medial collateral ligament at its attachment to the medial femoral condyle, and is usually considered to be the result of an old injury or sprain. There is another type of Bursitis that occurs over the medial side of the knee: Pes Anserine Bursitis/Tendinitis. This is a tendinitis and bursitis problem related to the medial hamstring tendons (Pes Anserine) where they wrap around the medial side of the knee to attach to the tibia. In doing so, they cross over the medial collateral ligament, which is where the bursitis/tendinitis occurs at the flare of the tibia. This particular Code, M76.4 _, does not seem to include this diagnosis, nor does ICD -10 in any way. As such, I would probably use the code M77.8 _: Other Enthesopathy, not elsewhere classified.
    • M76.5 _: Patellar Tendinitis, which is tendinitis over the course of the patellar tendon from the lower pole of patella to its insertion on the tibial tubercle. This would include "Jumpers Knee."
  • M79: Other Soft Tissue Disorders, NEC:
    • M79.2: Neuralgia/Neuritis NEC: There is a type of neuritic pain that occurs in the knee particularly involving the branches of the Saphenous Nerve that cross the front of the knee that give sensation/feeling to the skin over the front of the knee, particularly the infrapatellar region. This "Neuritis" is usually the result of some previous trauma, frequently minor trauma such as a contusion of the anteromedial aspect of the knee. The contusion of the nerve causes pain, burning, tingling, paresthesias, and possibly areas of numbness or loss of feeling across the front of the knee in the infrapatellar region. It can also be seen after knee surgery when the incision was made around the medial parapatellar region, the most common location of major knee incisions. This can result in a neuroma of these infrapatellar branches causing localized pain, tenderness, and shooting paresthesias with gentle palpation or percussion over the neuroma. I would consider this code for chronic "neuritic" situations.
    • M79.4: Hypertrophic Infrapatellar Fat Pad (Hoffa's Disease): There is a fat pad that lies behind/deep to the patellar tendon in the front of the knee. This can become inflamed and enlarged causing localized anterior knee pain.
    • M79.5: Residual Foreign Body in Soft Tissues: These can result from trauma to the knee, particularly falls in which the patient lands on the front of their knee on rough ground or terrain. The foreign bodies can be glass, metal, gravel, etc., embedded in the abrasions and/or lacerations, and which can remain after the skin has healed causing localized pain and tenderness.
    • M79.6: Pain in the Limb: This Excludes Knee joint pain (M25.56). Pain in the region of the knee could be a manifestation of a problem in the thigh (M79.65) or the knee and lower leg (M79.66). This is a regional pain, and is not very specific. I would use this only as a last resort.

Osteopathies and Chondropathies (M80-M94):

  • Disorders of Bone Density and Structure (M80-M85):
    • M80.0: Osteoporosis with Current Pathologic Fracture and M80.8: Other Secondary Osteoporosis: Patient's with advanced Osteoporosis of either of these two types could develop knee pain as result of what most of us would consider relatively minimal or minor trauma, such as a misstep or twist, resulting in an osteochondral fracture of either the distal femoral condyle or the proximal tibial plateau. These fractures may not even appear on standard x-rays, but may only be detectable on MRI or CT scans. Depending on the type of Osteoporosis, the code for a distal femur fracture would be M80.05 _ _ or M80.85 _ _ , and for the proximal tibia would be M80.06 _ _ or M80.86 _ _. These are 7 Character codes, with the 6th Character for Laterality, and the 7th Character options of A, D, G, K, P, and S.
    • M84: Disorder of Continuity of Bone:
      • M84.3: Stress Fracture (Fatigue, March, Stress Fracture/ Reaction): These fractures result from and require a significant change in a patient's activity and stress level for these to occur in normal, healthy bone. These do not occur in pathologic bone. They could occur in the distal femur and/or the proximal tibia, but are quite rare when compared to other sites in the femur or tibia. M84.35 _ _ would be for the femur , and M84.36 _ _ for the tibia. The 6th Character would be for laterality, and 7th Character options of A, D, G, K, P, and S.
      • M84.4: Pathologic Fracture, NEC, M84.5: Pathologic Fracture in Neoplastic Disease; and M84.6: Pathologic Fracture in Other Disease could always a cause of knee pain if the distal femur or the proximal tibia are the site of pathology or neoplasm. If possible, the neoplasm and/or the other source of pathology should also be coded.
      • In the M84.4 Code Set, M84.45 _ _ would cover the distal femur, and M84.46 _ _ the proximal tibia.
      • In the M84.5 Code Set, M84.55 _ _ would cover the distal femur, and M84.56 _ _ the proximal tibia.
      • In the M84.6 Code Set , M84.65 _ _ is for the distal femur, and M84.66 _ _ for the proximal tibia.
      • These all require a 7th Character, with the 6th Character being for laterality.
    • M85: Other Disorders of Bone Density and Structure:
      • M85.0: Monostotic Fibrous Dysplasia: The lesions of this disorder can occur in the distal femur and/or the proximal tibia and fibula. They may vary in size and are benign. They are a possible cause of pain, but probably not. These lesions are often seen on plain x-rays, and may be reported as "Nonossifying Fibroma" in the bone. M85.05 _ would be for a lesion of the distal femur , and M85.06 _ for the proximal tibia and/or fibula, with a 6th Character for laterality.
      • M85.4: Solitary Bone Cyst: These lesions can occur in many bones including the lower femur and proximal tibia and fibula, and could be a source of knee pain. Interestingly, M85.45 _ is for the pelvis, and does not seem to include the femur. There is no code designation for the femur, so I would include femoral lesions in this coding. M85.46 _ would cover the proximal tibia and/or fibula. However, the knee region is not a common site for these lesions.
      • M85.5: Aneurysmal Bone Cyst: Generally speaking, these are quite rare in the distal femur or proximal tibia, but anything is possible. M85.55 _ would be for the distal femur, and M85.56 _ for the proximal tibia and fibula. The 6th Character would be for laterality.
      • M85.6: Other Cyst of Bone: As usual, "Other" implies "None of the above," and would cover any other possibilities occurring in the distal femur and/or proximal tibia and fibula. Again, these are infrequent in either of these locations.
      • M85.8: Other Specified Bone Disorders of Bone Density and Structure: This includes Hyperostosis of bone and Acquired Osteosclerosis. For what it is worth, these are x-ray findings and are not in and of themselves a cause for local pain in the knee if found in the lower femur and proximal tibia.

Other Osteopathies (M86-M90): This group of codes contains many forms of bone pathology that can occur in and around the knee region, and could be the cause of knee pain such as Osteomyelitis and Osteonecrosis (of the various forms).

  • M86: Osteomyelitis: All of the variations listed in ICD-10 for this Code Set can occur in the distal femur and/or proximal tibia and fibula. They require a 5th Character: 5 for femur, 6 for the tibia and fibula, and a 6th Character for laterality. In general Acute is for 0-14 days, Subacute for 2-7 weeks, and Chronic for over 7 weeks of duration. These also require the coding for the infectious agent.

  • M87: Osteonecrosis, Avascular Necrosis of Bone: This includes Idiopathic (M87.0), Due to drugs (M87.1), Due to previous trauma (M87.2), Other Secondary Osteonecrosis (M87.3), and "Other" Osteonecrosis (M87.8). In general, the distal femur and proximal tibia are not common sites for any of these varieties, but they can occur. I am not sure whether M87.1: Secondary to drugs, includes Chronic Alcoholism, but it certainly could apply to chronic steroid use. These do require an additional code for the adverse effect, if applicable, and for the drug (T36-T50). As for M87.3: Other Secondary Osteonecrosis, I would probably use this for Alcohol related osteonecrosis, which can occur in multiple sites, and when severe and advanced, can include the distal femur for the knee region. This code group could be used for Sickle Cell Disease when Osteonecrosis occurs in the distal femur or proximal tibia. The other and probably better option for this would be M90.5: Osteonecrosis in Disease Classified Elsewhere, which includes Hemoglobinopathies (D66 & D67 Code Sets). Diseases included in M87.3 require Code also the underlying disease. For all of these Code Sets, the 5th Character is 5 for the femur, and 6 for the proximal tibia and fibula, and the 6th Character is for laterality.

  • M88: Osteitis Deformans (Paget's Disease of Bone) is uncommon in the lower thigh or upper lower leg, but could occur. This is not the same as that related to neoplasm (M90.6). The 5th Character 5 denotes the distal femur, and 6 for the upper tibia and fibula. The 6th Character is for laterality.

Chondropathies (M91-M94):

  • M91: Juvenile Osteochondrosis of the hip and pelvis (4th Characters 1, 2, 3, 4, & 8) are mentioned in this Blog mainly because in growing children, disorders of the hip joint or proximal femur can result in "Referred Pain," and present themselves as knee pain. These children may complain of pain in their knee before complaining of any pain in the hip region. The 5th Character is for Laterality.
  • M92: Other Juvenile Osteochondroses: This includes M92.4 _ for the Patella (Kohler, Sindig-Larsen) and M92.5 _: Proximal Tibia which includes Blount's Disease and Osgood-Schlatter's Disease at the tibial tubercle. The 5th Character is for Laterality.
  • M93: Other Osteochondropathies: This includes:
    • M93.26 _: Osteochondritis dissecans (Knee), which is seen in growing children and teenagers as a cause of knee pain. This usually occurs in the Medial Femoral Condyle, occasionally on the lateral side. The 6th Character is for laterality.
  • M94: Other Disorders of Cartilage: This includes:
    • M94.26 _: Chondromalacia of the Knee, but Excludes Chondromalacia of the Patella (M22.4). This can occur as the result of other joint disorders including trauma, and is often seen as an early stage of arthritis. It can be seen in association with chronic meniscal tears resulting in local damage to the adjacent articular cartilage. Although this Excludes Patellar Chondromalacia, it is certainly not rare for Chondromalacia to affect the femorotibial joint and the patella. As such, if both are affected, then separate codes should be used for each portion of the joint. I have also discussed this in a separate Blog regarding Knee Chondromalacia.

Knee Pain and ICD-10 (Continued)

Posted in Coding Blogs on May 26, 2017

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