The Soft Tissues in Osteoarthritis and Arthroplasty of the Hip

Abstract: Ultrasonography as a tool measuring the anterior capsular distance in THA was so far not described nor validated. Comparing the measurements of the capsular distance set with a caliper/ruler with those performed with ultrasonography on a THA model demonstrated a high correlation between measurements. The effect of experience of ultrasonography in THA was also evaluated comparing the first and last series of examinations. It was shown that intra/ inter observer agreement increased with increasing number of examinations. The pain in osteoarthritis (OA) and its relation to the elastic properties of the hip joint capsule was analyzed. In OA patients intracapsular pressure and capsular elasticity, i.e. compliance, was measured. Pain assessment, radiographic evaluation and ultrasonography measuring the anterior capsular distance of the hip joint were performed prior to these pressure measurements. No correlation was found between pain and intracapsular pressure in these OA hips. However, there was an inverse correlation between radiographic severity of OA and elasticity of the hip joint capsule. These findings indicate an increase in intracapsular pressure in early stages of OA and lower or no pressure in late OA. This observed lack of pain/pressure correlation was not in accordance with previous reports. These measurements were performed after the release of the short rotators. To investigate the effect of the short rotators on intracapsular pressure we investigated the pressure, pain and radiographic grade in OA patients. The pressure was measured in various positions of the hip before and after release of the short rotators. Release of the short rotators did not change the intracapsular pressure in any position except in 45° flexion, in which the pressure increased, nor did we find any correlation between pain and intracapsular pressure. Dislocation after THA is one of the most common postoperative complications. Postoperative intraarticular edema and/or fluid might be contributing factors. Posterior soft tissue repair was suggested to reduce the dislocation rate and decrease the volume of postoperative fluid in the THA hip. THA patients with or without posterior soft tissue repair were analyzed. To evaluate postoperative capsular distension, indicating synovial edema/fluid, US was performed 6 and 12 months after surgery. Posterior soft tissue repair resulted in greater sonographically measured capsular distance 6 months postoperatively, but after 12 months there was no difference in hips with or without posterior soft tissue repair. This finding suggests that the previously postulated idea that posterior soft tissue repair reduces postoperative “dead space can be debated. The role of synovitis and increased intracapsular hydrostatic pressure in the loosening process after THA has gained increased attention. Unrevised, radiographically stable hips that had THA because of osteoarthritis 10 years earlier with 28 or 32 mm femoral heads were analyzed. The correlation between PE wear and sonographically measured capsular distances was estimated. It was found that 32 mm femoral heads were associated with greater wear and greater capsular distance as compared to 28 mm heads. A correlation between linear and volumetric wear and sonographically measured capsular distance was also noted. These findings were observed before radiographic signs of loosening, and indicate that the THA loosening process starts before its radiographic appearance.