The purpose of the present investigation was to evaluate muscle damage one year after anterior minimally invasive THA by MRI and to compare these findings with MRI investigations performed in asymptomatic patients one year after THA using a conventional direct lateral approach.

Institutional review board approved this study and patients gave signed informed consent. The minimally invasive group consisted of a consecutive series of 25 patients 1 year after anterior minimally invasive THA. The historic control group consisted of a consecutive series of 25 asymptomatic patients (no pain, no limb, full abduction strength) 1 year after conventional THA. Excluded were patients having prior hip surgery or suffering lumbar spine pathology. Tendon defects and degenerations within the insertion of the Gluteus medius and minimus muscles as well as fatty atrophy within these muscles were recorded according to the protocol of Pfirrmann et al. A Mann-Whitney U Test, two sided t-test and Chi-square test were used for appropriate comparison of quantitative and qualitative variables, respectively.

In terms of gender, age, BMI and side no significant differences were shown between the two groups. When compared to the conventional group, tendon defects, diameter changes and signal alterations of the Gluteus medius and minimus insertion were significantly less frequent in the minimally invasive group (p= 0.001–0.03). Fatty atrophy within the gluteus minimus and gluteus medius musculature was significantly less in the minimally-invasive group (p=0.001–0.04).

In terms of structural damage to muscles and tendons of the hip abductors, the anterior minimally invasive approach proves to be less invasive than the direct lateral approach.

Background: Femoroacetabular Impingement is now considered a prearthritic hip mechanism. It frequently occurs in patients with subtle anatomic abnormalities of the acetabulum, “acetabular retroversion”, which is often difficult to detect on standart xrays. Early diagnosis is of utmost importance as surgical intervention in early stages can most likely halt progression of disease. The objective of this study was to assess wether an easily visible anatomic landmark on an anteroposterior (AP) pelvic xray can be used to screen patients with acetabular retroversion.

Methods: The AP pelvic xrays of 1010 patients who were seen at the autors’ institution for a painful hip were reviewed over a 16 year period. Those xrays that did not meet standardized criteria were excluded leaving 149 AP radiographs (298 hips) for analysis. The ‘crossover sign’ (COS), indicative of acetabular retroversion, was recorded for each hip. An easily visible landmark, the prominence of ischial spine (PRIS) into the true pelvis was also recorded and measured. Interobserver and intraobserver variability was assessed.

Results: The presence of the PRIS as diagnostic of acetabular retroversion showed a sensitivity of 91% (95%CI 0.85 to 0.95), a specifity of 98% (95% CI 0.94 to 1.00), a positive predictive value of 98% (95%CI 0.94 to 1.00), a negativ predictive value of 92% (95% CI 0.87 to 0.96). There was good and very good intraobserver and interobserver reliability for measurements of the COS and PRIS, respectively.

Conclusion: There was excellent sensitivity and positive predictive value of the PRIS as a radiographic marker of acetabular retroversion. The rims of the anterior and posterior walls are sometimes not clearly visible, and even if they are, their translation into a reliable interpretation of acetabular retroversion is difficult. The PRIS sign appears as a good visible prominence on the AP radiographs which can’t be easily confused.

The fear of high complication rates, repeated surgery and component mal positioning, especially early in the surgeon’s experience, can be an obstacle for starting a new technique like minimally invasive THR.

The aim of the present investigation was to report on our learning curve of the first 100 consecutive minimally invasive total hip replacements through an anterior approach and to focus on intraoperative and postoperative complications as well as on the quality of implant positioning.

In order to have a comparison, the last 100 THR performed through our previously used direct lateral approach were retrospectively evaluated. In both groups, complex acetabular and femoral reconstructions were excluded as they were performed though a digastric trochanteric osteotomy. Every change of the initial surgical plan was considered an intraoperative, every change in the rehabilitation plan considered a postoperative complication. The quality of implant positioning was evaluated in a standardized anteroposterior pelvic x-ray and a cross table lateral view at the 3 month follow-up visit and included the positioning of the cup and the stem in both views and the amount of leg-length discrepancy.

In terms of age, gender, BMI, ASA-score and origin of osteoarthritis both groups differed not from each other. Intraoperative and postoperative complications were more frequent in the MIS-Group (17 versus 7) and occurred within the first 30 cases. 12 were solved during the same anesthesia and 2 during the same day without manifest disadvantage at the 3 month follow-up visit. In one case a dislocation occurred. In two patients neuralgia of the lateral cutaneous femoral nerve was successfully treated conservatively. Implant positioning and leg-length discrepancy did not differ between the two groups.

Overall, starting a minimally invasive technique was associated with more frequent complications; however, if recognized and appropriately managed nearly none of them resulted in disadvantages for the patient at the 3 months follow-up visit.