Peter A. Huijbregts, PT, OCS, FAAOMPT
Abstract: Osteonecrosis of the humeral head may be idiopathic, but it is also associated with a number of known medical conditions. In these patient groups, it is a differential diagnostic possibility that the physical therapist needs to consider. This article discusses histopathology, classification, etiology, history and examination findings, and treatment of humeral head osteonecrosis. It also presents two case studies of patients with undiagnosed osteonecrosis who were referred to physical therapy to illustrate the difficulties and possibilities for correct identification of such patients.
Key Words: Osteonecrosis, Humeral head, Bone
Osteonecrosis is defined as the in situ death of cells within the bone due to a lack of circulation and not as a direct result of disease1,2. The cells involved may include osteocytes, both in cortical and cancellous bone, and hematopoietic and fat cells in the marrow cavity1. Osteonecrosis is also often referred to as avascular or aseptic necrosis1. However, osteonecrotic bone is not avascular: the blood vessels are still present, but circulation within them is compromised1. The term osteonecrosis is preferred to avascular or aseptic necrosis, as it gives the most appropriate description of the histopathologic process occurring but without suggesting a specific etiology1.
Central to the etiology of osteonecrosis is the compromise of circulation in the vessels supplying the bone. There are four mechanisms for such compromise1. Mechanical vascular disruption can result from fracture, dislocation, and fatigue fractures. Arterial occlusion can be caused by thrombosis, embolisms, and abnormally shaped cells. Injury to or pressure on the arterial wall may impair circulation in three different ways; this can occur from within the wall, as with vasculitis, or from within the vessel, due to release of vasoactive substances causing angiospasm. Extravasated blood, fat, or cellular elements may increase extravascular, intraosseous pressure and thus decrease circulation. Finally, occlusion of venous outflow may raise venous pressures over those in the arterial portion of the circulation resulting in compromised circulation to the cells.
Some 90 different bone necroses have been described in literature, all with similar radiologic and histologic findings3. Osteonecrosis may affect both epiphyses and apophyses3. Examples are Perthes’ disease affecting the epiphysis of the femoral head, Osgood-Schlatter’s disease affecting the tibial tuberosity, Koehler’s disease I affecting the second metatarsal head, Kienboeck’s disease or lunatomalacia, and Scheuermann’s disease affecting the vertebral epiphyses. Adler also classifies osteochondritis dissecans as an epiphyseal osteonecrosis. Subchondral areas are especially prone to osteonecrosis. Here arterioles assume a sinusoid course and are forced to make a 180 degree turn in order to return to the intraosseous circulation3,4, making them more prone to occlusion. A relatively small number of vascular foramina and a limited collateral circulation will further increase the risk of local ischaemia2.The femoral head is most frequently affected; next most commonly affected are the proximal humerus, and medial and lateral femoral condyles5. The proximal tibia, talus, scaphoid, lunate, and capitellum humeri can also develop osteonecrosis4,5.
In my clinical practice, I was recently confronted with two patients with therapy-resistant shoulder complaints. I referred both patients back to their respective physicians with requests for further diagnostic testing. Both patients were subsequently diagnosed with osteonecrosis of the humeral head and treated with a hemi-arthroplasty. They both regained nearly full function and reported minimal pain after a course of post-surgical physical therapy. In this article, I review the histopathology, classification, etiology, history and examination findings, and treatment options for osteonecrosis of the humeral head. I will also discuss the pre-operative presentation and clinical course for the two patients mentioned earlier. The intent of this article is to increase the awareness among physical therapists of osteonecrosis of the humeral head as a differential diagnosis for patients with complaints of shoulder pain and decreased range of motion.