BLOG: Cartilage health following trochleoplasty
by Ian D. Hutchinson, MD, MCh
There has been some concern about the long-term effects of the trochleoplasty procedure on articular cartilage health. While short-term studies have yielded encouraging results, there has been some heterogeneity with regard to the development of pain and arthritis in studies with a mean follow-up greater than 5 years.
In 2006, Philip B. Schöttle, MD PhD, and colleagues reported on cartilage viability and quality using histological examination of biopsies taken from three patients at 6 to 9 months following trochleoplasty. Overall, their findings suggested that cell viability and matrix architecture were maintained and that lacunae were in-growing from the underlying bone. Of some concern, there was a preponderance of chondrocyte loss from the superficial zone and chondrocyte clusters were demonstrated in one patient. These findings were complimented with promising clinical and radiological outcomes at 2 years and 5 years, being congruent with the literature.
While Schöttle’s paper addressed the question of acute cartilage damage, it falls short of prognosticating the health of the cartilage in the medium to long term. The cellular component of cartilage (1% to 2% chondrocytes) is responsible for homeostatic regulation of the low-turnover physiological condition evidenced by minimal collagen turnover and relatively more glycosaminoglycans turnover. Normal joint mechanical loading results in diffusion of molecules from the synovial fluid providing nourishment; the subchondral bone potentially provides an important source of nutrition to the deeper layers. Boundary lubrication is provided by lubricin produced by synoviocytes and superficial zone chondrocytes.
Clinical literature has demonstrated that the trochleoplasty procedure does not normally result in early catastrophic failure of the articular cartilage. This supports the aforementioned histological findings of viable chondrocytes within a maintained structural matrix with bone healing, allowing the cartilage to function as an articulating biomaterial. However, in the longer term, it is acknowledged that the operated cartilage has often been traumatized and/or pathologically loaded prior to trochleoplasty and may be susceptible to post-traumatic osteoarthritis. In addition, given the specific invasive nature of this procedure, alterations in structure and function of the osteochondral unit warrant consideration.
Cartilage-bone cross talk across the osteochondral junction has been implicated in pathophysiology of osteoarthritis and is thought to be mediated by soluble factors and direct cartilage to bone cell contact. Mechanically, bone is more adaptive than cartilage and subchondral remodeling to surgery or altered joint stresses may compound altered loading on the articular cartilage. Collectively, disruption of the osteochondral unit during trochleoplasty may alter cartilage loading, tissue homeostasis and nutrition. As a relatively low turnover matrix, the healed cartilage may function sufficiently in the short to medium term as an articulating biomaterial before increased demand and decreased maintenance of the matrix become clinically apparent.
As more robust longer-term data becomes available, the fate of the cartilage in trochleoplasty will become apparent. In the interim, research focused on the behavior of osteochondral unit and surgical techniques to preserve its functions are justified. Patients may also benefit from expanded rehabilitation protocols and life-long exercise regimes to promote sustained confidence, function and overall patellofemoral joint health.
Ian D. Hutchinson, MD, MCh, is a PGY-4 resident physician in the division of orthopedic surgery at Albany Medical Center in Albany New York.
References:
Cartilage viability after trochleoplasty. Schöttle PB, Schell H, Duda G, Weiler A. Knee Surg Sports Traumatol Arthrosc. 2007;15(2):161-167.
Goldring SR, et al. Nat Rev Rheumatol. 2016;doi:10.1038/nrrheum.2016.148.
Disclosure: Hutchinson reports no relevant financial disclosures.