Multiple hereditary exostoses (MHE) involves the hip joint in 30-90% of cases. The osteochondromas may be in the femoral neck, femoral head, or in the acetabulum. They cause impingement of the hip joint, limitation and loss of range of motion, pain, hip subluxation (partial dislocation), acetabular dysplasia, coxa valga, and osteoarthritis.
Resection of these osteochondromas has been limited by the fear of avascular necrosis (AVN). We treat these deformities with a varus osteotomy of the femur to correct subluxation and coxa valga, as well as to prevent acetabular dysplasia. This bends the femur inward towards the joint and restores proper alignment. Internal fixation is required to hold the alignment in place. We will also perform a surgery known as a Safe Surgical Dislocation (SSD), a procedure originally developed by Dr. Ganz in Switzerland.
During the SSD procedure, we will surgically dislocate the hip and excise the osteochondromas from the femoral head. Dislocation guards the circulation of the femoral head, which helps prevent avascular necrosis. We will also assess the sphericity of the femoral head and can perform a femoral head reshaping osteotomy to correct a femoral head that is not spherical. The SSD procedure has changed our ability to more extensively resect all of the offending osteochondromas with minimal risk of AVN.
We have a lot of experience with the Safe Surgical Dislocation surgery at the Paley Institute. The procedure is quite safe in our hands and is very successful. The recovery takes in total about 3 months, with half of that time in a custom-molded brace. It is not uncommon for both hips to require similar treatment; in such cases, the surgeries are staggered so that the second hip is only operated on once the first hip has fully healed. Physical therapy is also required during recovery time.
In a recent personal series, SSD was performed on 10 hips (7 patients) with MHE with resection of all offending osteochondromas. A prophylactic screw was used to protect the femoral neck. The mean follow-up was 5 years (range 2 – 9 years). The average age was 22 years (range 6 – 39 years). The ratio of the diameter of the femoral neck to that of the neck shaft ratio (NSR) as an index of femoral neck overgrowth and the amount of surgical excision were compared before and after surgery. The range of motion was also compared before and after surgery. Five of the patients had a varus osteotomy to treat a neck-shaft angle (NSA) of greater than 150°. The results of the study were as follows:
- Pain resolved in all cases
- Hip flexion improved from an average of 65° to 104°
- Significant improvement in hip rotation and abduction
- The NSR ratio significantly improved
- The NSA improved from an average of 157° to 139°
- No patient suffered AVN of the hip
- No patient suffered nonunion of the greater trochanter or the osteotomy
- No patient suffered a recurrence of osteochondromas
- One hip suffered an undisplaced fracture of the femoral neck six weeks after surgery during physical therapy
SSD has proven to be a safe, effective way to treat MHE of the hip and is safely combined with varus osteotomy techniques. The surgery comprehensively addresses the range of motion, subluxation, impingement, and neck shaft angle all in one procedure with minimal risk of AVN.