Medial Compartment Arthritis
Etiology
Osteoarthritis of the knee usually occurs secondary to mechanical factors, which include partial or complete meniscectomy, femoral osteonecrosis, lower extremity trauma, ligamentous laxity, obesity, and lower extremity malalignment.[1,2]
Pathophysiology
With removal of approximately one third of the meniscus, increased force is transferred directly to the tibial articular surface.[ 3]The joint also becomes less congruent and is not able to disperse the force across the joint. Both of these factors increase contact stresses, which can lead to articular cartilage damage and subsequent osteoarthritis.[3,4,5]
Results from multiple laboratory studies have shown that abnormal alignment also leads to abnormal contact stress. Ogata et al, Wu et al, and Reimann performed similar studies in which a varus stress was placed across the knee.[12] Each study documented degeneration of the articular cartilage in the medial compartment. The injury to the articular cartilage occurs in the deeper layers without any surface evidence of injury.[11,12]
Fractures of the tibial shaft and plateau may lead to subsequent lower extremity malalignment. Most clinicians accept less than 10° of angulation in tibial shaft fractures. For instance, residual varus angulation increases contact stresses across the medial compartment of the knee. Tibial plateau fractures also may lead to medial compartment osteoarthritis. The arthritis in this instance is due to direct articular cartilage damage caused by the intraarticular fracture.
Ligamentous laxity also is a cause of medial compartment osteoarthritis. Anterior cruciate and/or lateral collateral ligamentous laxity or incompetence has been implicated as causes for medial compartment osteoarthrosis. ACL-deficient knees allow for anterior subluxation of the tibia on the femur. This leads to increased shear force upon the articular cartilage, which leads to early degeneration of the articular surface.
Torsional deformities of the tibia and femur have a clinical association with the onset of medial compartment degenerative changes. The torsion may be present on the tibial or femoral side of the knee. This may lead to varus angulation and increased contact stresses across the articular cartilage of the medial joint space, which leads to accelerated medial compartment osteoarthritis.
Presentation
Patients generally present with a chief symptom of pain in the knee that has worsened over time. Patients state that the knee generally feels worse in the morning when they awaken and that the knee pain generally lessens with some activity. As their activity increases during the day, so does their pain. Patients may state that anti-inflammatory drugs help alleviate the pain. Patients frequently describe pain on the inside (genu varum) or outside (genu valgum) of the knee if unicompartmental arthritis is the cause of their symptoms.[9,10,11]
History and physical examination are crucial in making the diagnosis. It is important to ascertain whether trauma to the knee has occurred, indicating an old history of fracture, articular damage, and/or ligamentous injury and malalignment. A history of pain in other joints may alert the physician to an etiology of inflammatory arthritis or bilateral lower extremity malalignment.[9,10]
Physical examination may reveal varus or valgus alignment of the knee. Pain over the medial joint line may indicate a meniscus tear or degenerative changes within the medial compartment.[12] Patellar tendon tenderness also may indicate medial joint degeneration, as well as possible patellar tendon pathology. Patients may have crepitus in the knee. Range of motion (ROM) of the knee may be decreased compared to the opposite side. Fixed flexion contractures are uncommon but may occur in patients with tibiofemoral osteoarthritis. Evaluation of ligamentous stability is important. The integrity of the cruciate ligaments and collateral ligamentous stability may determine the feasible treatment options.[12,13,14,15]
Determining whether the patient with varus or valgus alignment of the knee can be passively corrected to neutral is of key importance.[14] Again, this aids in determining the surgical options for treatment of medial compartment disease.
Treatment Modalities
Multiple treatment options are available for isolated medial compartment osteoarthritis of the knee. Surgical intervention is indicated when conservative therapies have failed. Conservative therapies include nonsteroidal anti-inflammatory drugs (NSAIDs), joint viscosupplementation, unloading braces, and physical therapy.
Arthroscopy
The first operative procedure is knee arthroscopy. Arthroscopy is indicated for patients in whom conservative therapy has failed who want the most minimal surgical procedure available. Arthroscopy usually is used as a temporizing measure until definitive surgical treatment is undertaken. Knee arthroscopy sometimes is indicated as a diagnostic procedure to determine a treatment pathway or may be utilized in conjunction with a definitive procedure. Arthroscopy of the knee has not been shown to slow the course of osteoarthritis of the knee; however, it has been demonstrated to provide pain relief. The period of pain relief ranges from 6 months to a few years.[9 ]
Osteotomy
High tibial osteotomy (HTO) is indicated in patients younger than 60 years (ideally in their sixth decade of life) who are in labor-intensive fields and experience activity-related pain with a varus alignment of the knee. The arthritis in the medial compartment must be noninflammatory, and the patient should have no patellofemoral symptoms. Certain criteria regarding ligamentous stability and presence of minimal flexion contracture must be met. If this procedure is used alone, it should be considered a temporizing measure because joint resurfacing ultimately may be required.[5,13 ]
Arthroplasty
Unicompartmental knee arthroplasty is a surgical procedure used to relieve arthritis in one of the knee compartments in which the damaged parts of the knee are replaced. UKA surgery may reduce post-operative pain and have a shorter recovery period than a total knee replacements.[8] Also, UKA may have a smaller incision because the implants may be smaller.[8] Unicompartmental knee arthroplasty (UKA) is indicated in patients who are older than 60 years who have sedentary lifestyles, and were also performed for patients with age less than 60years noninflammatory arthritis, and pain with weight bearing[19]. Patients may have patellofemoral disease but usually are asymptomatic in that compartment. Symptomatic patellofemoral disease is a contraindication to the procedure. Ligamentous stability, weight, and coronal deformity of less than 15° also are considered. TKA is indicated in patients older than 65 years who have somewhat sedentary lifestyles and symptomatic arthritis in 2 or 3 compartments. The arthritis may be posttraumatic, degenerative, or inflammatory.[8,10,14,15,16,17 ,18, 19]


ABOVE:X-ray taken before arthroplasty(AP view and Lateral View)
BELOW: X-ray taken after arthroplasty(AP view and Lateral View)


Partial Knee Resurfacing Implant compared to a Total Knee Replacement Implant
Citation:
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