Introduction

The same cup orientation is classically applied to all cases of hip replacement (45° abduction, 20° anteversion). We hypothesize that this orientation must be adapted to the patient's hip range of motion. We tested this hypothesis by means of an experimental study with respect to hip range of motion, comparing the classical orientation (45° and 20°), and the orientation obtained with computer-assisted navigation.

Periprosthetic humeral fractures are rare but their numbers tend to increase because of the development of shoulder prostheses. We analysed our cases to see if some therapeutic guidelines can be provided.

Material and Methods: Our retrospective monocentric study included 12 patients (11 women, 1 man), with an average age of 76 (49 to 93). 9 were osteoporotic. All fell from their height except a polytrauma. They were operated from 1994 to 2007. 9 fractures were at the tip of the stem. 2 proximal, 1 distal, 10 prostheses were monopolar for previous proximal humeral fractures, 7 were cemented.

Results: Internal fixation was used in 8 cases with difficulties to find a suitable device in the first ones and LCP plates in the last ones. 4 cases had a prosthetic revision (with a humerotomy in one case): 2 monopolar long stems, 2 inverted prostheses (one with a long stem). Several complications were observed: 1 death (polytrauma), 3 radial palsies (which recovered), 1 sepsis (cured), 1 sympathetic dystrophy. The fractures healed at an average of 68 days (60 to 77).

Discussion: These fractures are little mentioned in the literature (15 references), often as case reports; the largest serie comprises 19 cases. The classifications, up to now, are descriptive not orientating the indication. Using a system derived from the SOFCOT 2005 symposium on periprosthetic fractures of the proximal femur seems efficient. A letter for the fracture site (A:metaphyseal, B: at the stem, C: distal) and a figure for the implant fixation (1: fixed, 2:loose, 3: with osteolysis) describe the situation. When reviewing retrospectively our cases we found that types A and C are generally not loose and that this classification gives a good guideline. For internal fixation, previous devices were poorly adapted. Now, LCP plates with locked screws and cables are preferred. In prosthetic revision, the choice between an anatomical or a reversed prothesis depends on the rotator cuff, the glenoid bone stock, and the patient general condition. A long stem is preferable (acting as a ‘nail’).

Conclusion: Regarding periprosthetic fractures, the proximal humerus can be considered as rather similar to the proximal femur. But the glenoid and the cuff may change the type of implant for revision.

Purpose of the study: Most systems used for computer-assisted total hip arthroplasty require preparatory computed tomography acquisition or use of multiple bone markers fixed on the pelvis. In order to overcome these problems, we developed a novel system for CT-free computer assisted hip surgery based on a functional approach to the hip joint. The concept is to orient the cup within a cone describing hip motion. The purpose of the present study was to analyze preliminary results obtained with this new system.

Material and methods: This new system was used to implant 18 primary total hip arthroplasties in 16 women and 2 men (mean age 68±7.8 years, age range 54–83 years) with degenerative disease. Two optoelectronic captors were fixed percutaneously on the pelvis and the distal femur. The acetabulum was reamed, then the femur prepared with instruments of increasing caliber. The last reamer positioned in the shaft carried an upper head which matched the size of the prepared acetabulum. Hip joint motion was recorded to determine the cone of maximal hip mobility. The system then oriented the cup so that this cone was completely included the cone described by the prosthesis.

Results: There was one traumatic posterior dislocation (fall in stairs) at three weeks, without recurrence. The Postel Merle d’Aubigné score improved from 8±2.9 (3–12) preoperatively to 17±0.8 (16–18) at last follow-up. None of the patients complained about the sites where the percutaneous markers were inserted and ther were no cases of hematoma or fracture. Mean leg length discrepancy was 5.6±7.5 mm (range 0–25 mm) before surgery and 0.6±3 mm (range −5 to 10 mm) at last follow-up. Mean anteversion of the femoral implant was 22.3±6.7° (14–31). Anatomic anteversion of the cup (measured from a marker linked to the pelvis and thus independently of the position of the pelvis) was 25.9±10.4° (12–40). The sum of the femoral and acetabular anteversions was 48.2±14.6° (range 27–71°).

Conclusion: This method can be used in routine practice without lengthening operative time excessively. It provides a safe way to control the length of the limb and helps position the cup. This study demonstrated that there is no ideal position for the cup that can be applied for all patients. Because of the wide spread of the inclination and anteversion figures, half of the cases were outside the safety range recommended by Lewinnek.

Purpose: This multicentric retrospective study was conducted to search for indications of femoral revision with a custom-made non-cemented implant.

Material and methods: We collected files on femoral revisions using custom-made implants among our working group and among surgeons having a certain experience between 1989 and 1991. Twenty-one patients (13 men and 10 women), mean age 50.1 years (24–81) were operated. This was the first revision for 14, the second for six, and the third for two. Mean follow-up was 35.4 years. The implant was coated with hydroxyapatite in the proximal zone with optional distal locking except for the first cases. The implant was used when the usual implants were poorly adapted. Data acquisition was achieved with previous calibrated computed tomography. The problem was to distinguish residual bone from cement or the prior implant. Information was exchanged between the engineer and the surgeon in order to define the stem shape and anchorage. Regular clinical follow-up was performed, noting the Postel Merle d’Aubligné score. The radiographic assessment focused on the absence of prosthesis descent and lucent lines.

Results: The PMA score improved from 9.6 (6–14; 2.4; 4.26; 2.91) to 14 (8–18; 4.61; 5.05; 4.25). Complications were dislocation in three hips, one requiring cup replacement and the other neck replacement. Early descent of the femoral stem was also noted in one hip which required revision. Late descent at 13 years was managed by a simple procedure in one hip (SOFCOT stage I).

Discussion: The early failures were related to the severity of the initial lesions (or rather their underestimation) and to defective initial distal stabilisation. Late failures resulted from the absence of bioreactive coating. We have had no experience with impacted grafting. The indication for custom-made implants are exceptional (less than 2% of our revisions) and can be divided into four categories: extramedullary (very long neck/varus) the implant avoiding the use of balls; extrapolation (femur too small or too large requiring under- or oversized implant); dysmorphism (excessive curvature, osteotomy or fracture sequelae, narrow metaphysic with wide diaphysis); gap filling (weight-bearing zone).

Conclusion: The advantage of a custom-made implant is the choice of anchorage and the simplification of the operative procedure. It is often the only solution in complex situations but requires close collaboration with the engineer (virtual intervention) and implies significant cost.

Aims: This prospective study investigated the possibilities of substitute osteointegration in an unfavourable environment. Methods: 26 patients aged 57 to 92 years (average 80) have been followed up from 6 to 24 months with serial AP and lateral X-rays. The acetabular damages were: 2 SOFCOT grade I, 9 grade II, and 15 grade III.Granules ofTriosite¨ þlled the cavitary defects mixed with and covered by cancellous bone. One pack was used 13 times; two,6 times; three, 6 times; and four, once. An HA coated hemispherical cementless cup was pressþtted, stable without screws 8 times. Results: In other cases the acetabular cup remained stable without any lucency. Disappearance of the granules was observed only 4 times. In 14 cases osteo-integration seemed in progress, but the granular shape was still discernable. In 8 cases, even at 2 years follow-up, the granules were well visible (those were cases of grade III defects). Conclusion: In acetabular revision of a total hip replacement, the size of the defect may need a large amount of cancellous autograft. Bone substitutes seem an elegant means of sparing the patientñs bone. The rstþpapers on this topic seemed rather enthusiastic, but our experience is more contrasted. It seems that the speed of resorption of this bone substitute be volume-dependant: the bigger the defect, the slower the osteo-integration. May be growth factors should be added to speed up the process.

Purpose: We performed mechanical trials to quantify the contribution of locking to the stability of revision femoral implants. The implant tested was a revision prosthesis with anatomic metaphyseal contact locked with three distal bolts measuring 4.5 mm.

Material and methods: Twelve implants were impacted into composite saw bones with constant and known dimensions and mechanical properties. Three displacement sensors were used to measure micromovements between the prosthesis and the bone: three specially designed force sensors were inserted into the bolt holes to measure the force distributions for each hole. Measurements were made with an Instron. Compression cycles (780 1-Hz cycles, 100daN applied to the femoral head) and torsion cycles (780 1-Hz cycles, 4.5 Nm applied to the femoral head) were used to simulate loading and weight-bearing and to estimate the evolution of the system. Trials were conducted in two different configurations: stable metaphyseal prosthesis, unstable metaphyseal prosthesis (simulating surgical resection). These two configurations were tested with a locked and with a non-locked implant.

Results: Loading distribution between the bolts was variable and depended on the insertion conditions, implant/bolt tolerance, and the quality of the supporting bone. In the “stable” metaphyseal configuration, the bolts carried a large percentage of the compression force (up to 30%) despite the support provided by the metaphysis; when exposed to torsion stress, the metaphyseal form of the prosthesis carried the charge and avoided this phenomenon. Locking had only minimal effect on micromovements, the impaction and the form of the prosthesis maintaining its stability. For the “unstable” configuration, locking created a stable situation: micromovements were limited to those observed in the stable prosthesis (< 150 μm), compatible with bone regrowth. The bolts carried most of the charge (74.8 ±20%; 56.0±41.7%) during the compression and torsion tests. Loading created major stress within the bolts whose properties (strict diameter 4.5 mm, lateral threading) should be taken into consideration to avoid risk of rupture beyond the elastic limit of the material.

Discussion: These results can be reasonably extrapolated to surgical situations leading to the following conclusions: locking is useful and reliable after surgical resection, all the holes available should be used for locking, “rational” unlocking can be useful if “physiological” metaphyseal stress is desired.