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Disease Progression

Disease Progression: Conservative and Hemiarthroplasty Treatments

The natural history of articular cartilage in human has not been well documented and clinical observations indicate that articulating cartilage lesions will frequently result in severe, persistent pain and functional impairment. When they are large, these lesions tend to progress in size, possibly to osteoarthritis within a relatively short period of time.

A recently published study in a goat model (D. Jackson) suggests a large grade IV osteochondral defect, will experience a progression of degenerative changes that occur around the rim of the defect and, in as little as one year, degrade the entire joint compartment. This study documented the progression of changes over the one-year period, including cartilage thinning, flattening, and destruction. At the one-year endpoint, the shape of the affected condyle was characterized by a loss of contour, condylar flattening and even collapse of the subchondral bone. In the graphic above the degenerative changes are shown from A to F with F being at the one year point.

This progression has been similarly predicted in finite-element models of osteochondral damage. These models have shown that compressive strains reach maximum values around the rim of a defect and that as defects become larger, the compressive strain values increase as well.

Using the previously mentioned study as a control, Arthrosurface evaluated the device design in a similar goat model to assess how safe and effective the HemiCAP implants might be in humans. In summary, the conclusion of the study showed that "The clinical outcome, gross appearance, and histologic data imply the biocompatability and functionality of the implant. Our data imply that the comparatively less traumatic resurfacing technique described here may serve as an interim treatment for these patients, possibly ameliorating the inflammation and pain of osteoarthrosis."

Perhaps the best indicator of the natural progression of large articulating cartilage lesions over an individual's lifetime is the Linden et al series in which patients with radiographic evidence of osteochondritis dissecans (OCD) were followed for over 30 years. Linden's series showed that patients who developed these severe lesions at an early age (23/67 knees), prior to closure of the epiphyseal lines, had a much better prognosis than adults (44/67 knees). Within the population diagnosed with OCD as children, only 2 knees had progressed to even mild gonarthrosis at approximately 30 years follow-up. In contrast, within the population diagnosed with OCD as adults, 14 knees had progressed to mild and 29 knees had progressed to severe gonarthrosis, at approximately 30 years follow-up. Linden concluded that trauma as a causal factor was supported within the adult population, and that the borderline between OCD and osteochondral fracture was not well defined in the adult population. Interestingly, Linden also noted that the onset of symptoms of pain and radiographic evidence of gonarthrosis did not appear in these patients until an interval of approximately 20 years had passed.

Patients presenting with the early symptoms and radiographic evidence of articulating cartilage injury may be initially managed with conservative, non-surgical treatment including weight reduction, physical therapy to increase support musculature, unloading braces and medications. Medications such as nonsteroidal anti-inflammatory drugs (NSAIDS) have not been shown to be any more effective than simple analgesics such as acetaminophen.