Bone density changes following surgical correction of femoroacetabular impingement deformities

OBJECTIVE

Femoroacetabular impingement (FAI) involves abnormal hip biomechanics due to deformities and is associated with osteoarthritis. Bone mineral density (BMD) in the acetabulum is higher in subjects with convex femoral (cam) FAI deformities compared to control subjects. The objective of this study was to assess post-operative changes of BMD with and without surgical correction of the cam deformity.

DESIGN

Thirteen patients with bilateral cam deformities but unilateral symptoms underwent pre-operative and follow-up computed tomography (CT) scans of both hips. The deformity was surgically removed from the symptomatic hip. BMD was measured in regions of interest (ROI) around the superior acetabulum from CT scans at both time points. The contralateral untreated hip was used as a within-patient control. Changes in BMD were assessed by two-way repeated measures ANOVA (side, time) and paired t-tests.

RESULTS

A greater BMD decrease was seen in the treated compared to the untreated hip (P < 0.0018). BMD within the superior acetabulum decreased by 39 mg/cc on the treated side (P < 0.0001) but only 9 mg/cc (P = 0.15) in the untreated contralateral hip. These changes represent 7.1% and 1.7% of the pre-operative BMD on the respective sides.

CONCLUSIONS

BMD decreased in the treated hip, suggesting a positive effect of surgical correction in relieving stresses within the hip joint. Longer term follow-up is required to assess the ultimate fate of the articular cartilage within the joint. This study showed that surgical correction of the cam deformity in patients with FAI may alter the pathological biomechanics within the joint.

MR Imaging of the Achilles Tendon after Surgical Repair

Achilles tendon tear is common and increasingly frequent. Magnetic resonance imaging (MRI) is the modality of choice for radiological evaluation. It is accurate to assess the status and integrity of the tendon with well documented features. In this article, the MR findings of a normal Achilles tendon as well as common diseases like insertional and noninsertional tendinosis, chronic tendinosis with marked lengthening, tendon rupture are illustrated. After a torn Achilles tendon receives surgical repair, it undergoes different stages of healing process including inflammatory, reparative and remodeling phases. Acute scar tissue in the surgical bed may share similar MR features of tendon re-rupture especially in the early healing phase because both are T2W hyperintense. The size of the gap may even appear larger than expected on T2W images possibly due to tendon remodeling. Understanding of the healing process in post-operative period may prevent overestimation of tendon gap and misdiagnosis of re-tear. We describe the MR features of the post-operative changes with serial studies in different months after surgery. The MR findings with the highlights of the expected sequential changes in normal healing process are illustrated in different cases. A case with surgical repair on a partial tear of Achilles tendon is also included.