Purpose: Precise biomechanical reconstruction of the hip joint by a hip arthroplasty is essential for the success of this procedure. With the increasing use of surface replacement arthroplasty (SRA), there is a need for better understanding of the key factors that influence the anatomical and the biomechanical parameters of the resurfaced hip joint. The goal of this study was to examine the influence of SRA on the vertical and horizontal offset of the hip.

Method: Twenty-one hips from 12 embalmed cadavers were resurfaced with a Birmingham Hip resurfacing. The thickness of the acetabular bone was measured pre- and post-reaming in 6 acetabular zones. Radiographs were taken before and after the procedure with a scaling marker. For statistical analysis, the paired Student’s T-test with a confidence interval of 95% and a significant p-value of p< 0.05 was used.

Results: The mean acetabular bone loss was 3.8 mm, 5.9 mm, 9.3 mm, 10.6 mm, 8.5 mm and 3.6 mm in zones 1 to 6. The “polar length loss” is the cumulative displacement of the femoral and the acetabular articulating surface in zones 2 to 5. This displacement indicates a shortening of the neck plus a medio-cranial displacement of the acetabular articulating surface and was 4.3 mm, 7.5 mm, 9.4 mm and 7.7 mm (zone 2–5). The radiographic center of rotation (COR) was significantly medialised (mean 6.2 mm) and displaced in the cranial direction (mean 6.9 mm) (p< 0.00001). The mean total (femoral plus acetabular) horizontal and vertical offset change was 6.4 mm and 9.5 mm respectively (p< 0.00001). There was a significantly higher vertical offset change in the acetabulum than in the femur (p=0.0006). This resulted in a significantly larger change in vertical than in horizontal offset (p=0,04).

Conclusion: The displacement of the acetabular COR was responsible for 60% of the total vertical and 99% of the total horizontal offset change. The femoral side did not compensate for this displacement. SRA did not restore the biomechanics of the native hip.

Purpose: Plate and cable alone constructs to treat periprosthetic fractures around a well-fixed femoral stem in total hip replacements, have been reported with high failure rates. The aim of this study was to evaluate the results of our surgical treatment algorithm to reliably use lateral plate and cable constructs in these fractures.

Method: One hundred and six periprosthetic fractures in 102 patients were treated between 1996 and 2006. Forty-five fractures were pre-operatively assessed as Vancouver type B1 fractures. The joint was always dislocated and stability of the implant was meticulously evaluated. This led to the identification of nine (20%) unstable stems leaving 36 fractures to be real B1-type fractures. The fracture was considered to be suitable for lateral plate and cable alone fixation if the medial cortex was not comminuted and an anatomical reduction of the medial cortex could be achieved. Twenty-nine B1- and 5 C-type fractures had been treated with a single lateral plate and cable construct. The mean length of follow-up was 43.2 months. The paired Student’s T-test with a confidence interval of 95% and a significant p-value of p< 0.05 was used to compare the pre- and postoperative UCLA hip scores.

Results: Four (12%) patients died within one month from surgery leaving 30 patients for follow-up. Twenty-nine fractures united at a mean of 6.4 months. One B1-type construct failed due to inappropriate proximal fixation. Two fractures united uneventfully with a mean of 8° of varus alignment of the proximal fragment. One patient with a C-type fracture sustained a fracture distal to the tip of the plate. There were three plate infections (8.8%). There was no significant difference between the pre- and post-operative UCLA hip scores (25 versus 23 resp.).

Conclusion: These fractures represent a difficult problem with a high complication rate of 30%. The presented treatment algorithm contributed significantly to the 97% union rate with plate and cable alone constructs that was comparable to the union rates achieved with combined plate and strut graft fixation.

Aim: Component positioning may be adversely affected by minimally invasive approach in total hip replacement due to restricted visualization. Problems with proper alignement are suggested to concern anteversion more than inclination and occur particulary in the lateral position.

Method: 53 patients were enrolled prospectively randomised to each group. First group (standard group, n= 30pts) underwent conventional total hip replacement in supine position and transgluteal approach and second group (MIS group, n= 23pts) underwent THR using minimally invasive anterior approach in lateral decubitus position Every group was operated on by two experienced senior surgeons. Desired cup position was 40°–45°inclination and 15–20° anteversion for the MIS group and 45°inclination and 15 ° anteversion for standard group. Postoperatively all patients had pelvic CT scan. Inclination and anteversion were determined by an independent observer using a 3-D model and planning software, the operative definition was used according to Murray.

Results: Mean inclination/anteversion in the MIS group was 39°(26°–50°)/25°(10°–47°), and 44°(29°–57°)/22°(1°–53°) within the standard group. Standard deviation for inclination was 7° for both groups, and 10° (MIS group) vs 14° (standard group) for anteversion.

The difference in the mean values regarding inclination was greater than would be expected by chance; there was a statistically significant difference (P = 0,010).

Discussion: In general cup positioning in both groups was less steep and more anteverted as presumed. The standard deviation for inclination was the same in both groups, but the standard deviation for anteversion was less in MIS group, that means less outliers regarding anteversion. Cup positioning in minimally invasive total hip replacement is safe compared to traditional approach.

Navigation technique was discussed to equalize the drawback of MIS. However, tools like imageless navigation may further improve the cup position even in traditional approach.

Introduction: The Birmingham Hip Resurfacing (BHR) is the most commonly used hip resurfacing for the treatment of hip osteoarthritis. The goal of this study was to evaluate how the surgeon could influence the biomechanical features of the navigated and non-navigated resurfaced proximal femur. METHODS 20 Cadaver hips were resurfaced with a BHR using femoral navigation. The native anteversion and neck shaft angle as indicated by the navigation system were used as a reference. The non-navigated femoral component jig was first placed in the “ideal” position aiming for 10° of valgus and neutral anteversion. The jig was then displaced 5mm in 4 directions. The anteversion and stem shaft angle (SSA) angle were measured for each position using the navigation system. A scaled XR was taken pre- and post-operatively. For statistical analysis, the paired Student’s T-test with a confidence interval of 95% and a significant p-value of p< 0.05 was used.

Results: The centre of rotation (COR) of the navigated resurfaced femur was 3,5 mm significantly (p=0,0006) more distal in the femoral neck than the native COR. This resulted in a 2.1 mm vertical caudal drop (vertical offset) and an average 2.7 mm lateral displacement of the COR (horizontal offset). The same measurements were done with 5° increments of the SSA from 120° to 140°. The vertical offset loss increased non-significantly (1.7 to 2.6 mm). The horizontal offset loss decreased non-significantly (3 to 2.2 mm). The native vertical and horizontal offset could be restored if 5 mm less bone was taken off the femur. The offset loss was significantly increased if 5 mm more bone than the normal reaming had been taken off (p< 0.0001). The “ideal” jig position on the lateral femoral cortex led to an average 137° SSA. Five millimetres of jig displacement on the lateral cortex in either direction did not lead to significant changes in the SSA or anteversion angles relative to the “ideal” position (all p> 0,13). Five millimetres of posterior displacement resulted in an average 139° SSA and 5,8° of anteversion in 95% of hips.

Conclusion: Surgical interventions can significantly change the biomechanics of the hip. Increasing the SSA with a fixed femoral head entry point, as often is done with navigation, does not significantly change the femoral offset. If the surgeon decides to take less bone off the femur, then the offset could be restored and even increased to 1 mm more than the native femur. If due to pathologic changes the bone loss would be increased to 5mm more than the “normal” bone loss, a significant offset loss of > 5 mm could be expected which might lead to detrimental biomechanical effects. The positioning of the jig is subject to surgical errors. The effect of a 5 mm error in either direction does not lead to significant changes in anteversion or SSA. Posterior displacement led to the most reproducible component positioning.

Objectives: Critical analysis of the results of 1124 patients over 70 years of age treated with an endoprothesis between 1987 and 2000. Patients: Patients over 70 years of age presenting a non-pathological unstable fracture of the femoral neck. Intervention: Depending on age and functional status preinjury, 715 times a hemi-arthroplasty; 409 times a total hip prosthesis. Main outcome and measurements: Evaluation of the functional status of the patients preinjury based on walking capacity and ability to perform some activities of daily life. Prospective follow-up of all surviving patients during the first postoperative year. Special attention to the local complications needing reintervention. The final functional evaluation in 708 surviving patients preoperatively classified as “independent”. Estimation of the revision arthroplasty rate and functional status of patients operated before 1995. Results: The overall mortality rate after 1 year: 20%. Complications after prosthetic replacement are not harmless: dislocation (2%) needing an early revision arthroplasty in about 50% of the cases; deep infection (< 1%) leading to a Girdlestone situation and sometimes even death. In 32% of the surviving patients preoperatively classified as “independent” the femoral neck fracture had caused an important additional impairment. Failure rate of prosthetic replacement for fractures much higher than after replacement for arthritis: at least 14% within five years. Conclusion: In patients younger than 70 years of age with a good life expectancy, prosthetic replacement has to be avoided whenever possible.

Aims: to evaluate the efþcacy of this technique in 46 tibias and 22 femurs with a delayed bone healing (> 6 months) with a minimum follow-up of one year after injection. Methods: Forty-þve injections were performed in a one-day clinic. At least 300 ml autologeous bone marrow is aspirated from the iliac crest using multiple aspiration sites. Through isopyknic centrifugation the mixture of bone marrow and phosphateÐbuffered saline was layered over undiluted Ficoll-Paque. Centrifugation was done for 35 min. at 400 times gravity. An average of 52 cc of mainly myeloid cells were obtained with a nucleated recovery rate of average 62% (27–90%). In 21 cases additional surgery was performed at the moment of bone marrow grafting. Eleven times an implant exchange, seven dynamisations and 3 additional bonegrafting. The bone marrow grafting was performed through cannulated screws seated in the medullary cavity below and above the fracture site. Results: we encounter one postoperative irritation of the pes anserinus tendons due to inþltration. Despite the fact that we aspirated an average of 340 cc of bone marrow no adverse reaction was seen from this nor from the sometimes forceful injection of 50 cc concentrated bone marrow. In eight cases no bone healing occurred. In þve cases, probably due to a lack of stability and implant failure. Conclusions: the use of concentrated bone marrow injected in the medullary cavity near the fracture site is cost effective and seems to give favorable results.