How Do You Manage the Patient Who Has Early Degenerative Joint Disease and Has Complaints of Pain and Instability?
First of all, the incidence and risk of degenerative joint disease of the anterior cruciate ligament (ACL)-deficient knee is significant, particularly with concomitant injury to the menisci and articular cartilage. In addition, a patient with predisposing factors such as preexisting varus alignment of the knee and who suffers ACL disruption may be at increased risk due to loss of some neuromuscular control of the knee.1 This loss of control allows the knee to go into a little bit more varus and, therefore, overload the medial compartment with a higher risk of chronic medial compartment overload and degeneration. The ACL does provide neuromuscular feedback and mechanically does provide some varus control of the knee. Therefore, with chronic ACL instability, the development of further varus deformity will often result in further medial compartment overload. As a result, it is not uncommon to encounter patients who have early degenerative joint disease complaining of medial joint pain and overload as well as instability in the setting of ACL deficiency.
The typical wear pattern in these knees involves the medial compartment located more posteriorly on the tibial plateau. This occurs because of the chronic anterior subluxation of the tibia dynamically with respect to the femur. The wear pattern may be even further posterior in the setting of medial meniscal deficiency (Figure 39-1).1 In addition, there is probably an age-related pattern in which the degeneration will be worse in the older patient population compared to the younger subacute and early post–ACL-injury group. As the arthritic changes in the medial compartment progress, the true instability of the knee usually becomes less of an issue due to the decreased motion, development of osteophytes, and contractures around the knee that occur with progressive arthritis. The instability symptoms from the ligamentous component become less prominent, although the patients may develop pseudo-instability symptoms from the arthritic change and catching from the irregularity of the degenerative joint surface. Therefore, the younger patient who has ACL instability with some degenerative joint disease likely has instability secondary to ligamentous laxity. The older patient who has more prominent arthritic change will likely be suffering more from the arthritic changes rather than the true ligamentous laxity.
Figure 39-1. (A) AP x-ray showing medial comp narrowing, osteophytes, varus alignment 4 years post-ACL injury. (B) Lateral x-ray showing posterior subluxation of the femur on the tibia.
In approaching these patients it is very important to clearly examine and delineate the problem that they are having with their knees. As mentioned above, it is important to outline what is giving them the symptoms—is it the actual giving-way and ligamentous instability or is it the painful problems from the degenerative joint disease, which may cause some symptoms of pseudo-instability? It is important to determine whether the degenerative change is only in the medial compartment versus the other compartments and whether the degenerative change is minimal or advanced. If the patients are having true ligamentous instability, then they will usually complain of this during more aggressive activities where the instability is evident, such as those involving some form of pivoting activity. Patients with isolated chronic ACL instability may have symptoms during activities of daily living or straight ahead function, but this is unlikely. If they are having symptoms from those daily activities, it is important to rule out a degenerative meniscus or articular irregularity causing some sort of pain that leads to the instability episodes.
Putting this all together, a 25-year-old patient, for example, would be more likely to be unstable and have ligamentous laxity causing the episodes rather than the 45-year-old or older patient who has been chronically ACL deficient who is likely not as active, will not be stressing his knee, and probably will be suffering more from the degenerative changes of the knee rather than the ACL instability.
Imaging should include radiographic evaluation, including routine standing anteroposterior (AP) views of both knees, the flexed-knee standing view to outline the amount of articular cartilage wear, bilateral skyline, or Merchant views and bilateral long-leg views from the hips to the ankles to determine the mechanical axis deviation. It is important when taking the bilateral standing views from hips to ankles that the patient is standing comfortably and feet are pointed straight ahead and that the x-ray technician does not force him to put his knees together, which may reduce the true varus deformity (Figure 39-2).
Figure 39-2. Double-leg standing demonstrating the mechanical axis in the med compartment in an ACL-deficient patient.
If the patient then is diagnosed with a chronically ACL-deficient knee with some early medial compartment arthritis and varus malalignment with overload, the treatment would be to optimize a nonoperative regimen including muscular rehabilitation, reducing the pain and inflammation from the degenerative joint disease, or consider bracing with an unloader-type brace to unload the medial compartment as well as controlling the instability symptoms from the ACL. After these nonoperative options have been employed and the patient continues to be symptomatic, one could consider arthroscopic evaluation of the knee with debridement of any loose articular cartilage or degenerative menisci along with exam under anesthesia to determine the need for further surgery.
Typically, the type of patient that one will be faced with is the chronic ACL-deficient patient who may have had a partial medial meniscectomy and has mechanical axis deviation into the medial compartment with some early medial compartment degenerative change. In this situation, I would consider doing a high tibial osteotomy to correct the mechanical overload and treat the early degenerative change. I would do an arthroscopy at the time of the high tibial osteotomy and address any loose articular cartilage or menisci. I would consider a concurrent ACL reconstruction in the younger patient who is much more aggressive and does suffer from true instability. In general, in the older patient who is suffering from mechanical overload and pain, most patients respond well to osteomy alone, although ACL reconstruction can be considered as a secondary procedure if instability persists.
Clatworthy M, Amendola A. The anterior cruciate ligament and arthritis. Clin Sports Med. 1999;18(1):173-198, vii.