The 3D interplay between femoral component placement on contact stresses and range of motion of hip resurfacing was investigated with a hip model. Pre- and post-operative contours of the bone geometry and the gluteus medius were obtained from grey-value CT-segmentations. The joint contact forces and stresses were simulated for variations in component placement during a normal gait. The effect of component placement on range of motion was determined with a collision model. The contact forces were not increased with optimal component placement due to the compensatory effect of the medialisation of the center of rotation. However, the total range of motion decreased by 33%. Accumulative displacements of the femoral and acetabular center of rotation could increase the contact stresses between 5–24%. Inclining and anteverting the socket further increased the contact stresses between 6–11%. Increased socket inclination and anteversion in combination with shortening of the neck were associated with extremely high contact stresses. The effect of femoral offset restoration on range of motion was significantly higher than the effect of socket positioning. In conclusion, displacement of the femoral center of rotation in the lateral direction is at least as important for failure of hip resurfacings as socket malpositioning.

In total hip replacement (THR), the initial fixation of the femoral stem has a critical influence on its long term stability. Objective intra-operative assessment of primary stability is a challenge, surgeons having to rely mainly on their clinical experience. Excessive press-fitting of the stem can cause intra-operative fractures in up to 30% of revision cases. In a previous study we demonstrated the feasibility and validity of a vibrational technique for the assessment of the femur-stem fixation in vitro.

In this in vivo study the vibration analysis was applied for the per-operative assessment of stem fixation in 30 THR patients who obtained an intra-operatively manufactured, hydroxyapatite coated, cementless prosthesis.

The surgeon inserted the stem through repetitive controlled hammer blows. After each blow, the frequency response function (FRF) of the stem-bone structure was measured directly on the prosthesis neck in the range 0–10 kHz. The hammering was stopped when the FRF graph did not change anymore. Extra blows would not improve the stability but would increase the fracture risk.

In 26 out of 30 cases (86.7%), the correlation coefficient between the last two FRFs was above 0.99 when the insertion was stopped. In four cases, when the surgeon decided to stop the insertion because of suspected bone fragility, the final correlation coefficient attained lower values.

During the insertion of a cementless prosthesis, the changes of boundary conditions and implant stability between subsequent stages are reflected by the FRF evolution. The higher resonance frequencies are more sensitive to the stability change. The correlation between successive FRFs can be used as a criterion for the detection of the insertion endpoint. Moreover, the FRF analysis can be used to detect dangerous situations during surgery like stem blockage and fracture risk. This study should be completed and validated by a post-operative follow-up of the patients.

We report the follow-up of a cohort of 86 patients who underwent total hip replacement (THR) with custom-made stem prosthesis. Fixation mode, cemented (group 1) or uncemented (group 2) is based on the bone quality. Aspects of physical health and changes in mental health are documented using 3 patient-administered questionnaires, pre-operatively and 6 weeks, 3, 6 and 12 months post-operatively.

Harris Hip Score (HHS), Hip disability and osteoarthritis outcome score (HOOS) and SF-36, multi-purpose, short-form health survey were used.

Globally HHS increases significantly (p< 0.01). In group 1 up to 3 months post-operatively and in group 2 up to 1 year. (p < 0.05). In group 2 HHS is significantly higher 6 months and 1 year postoperatively (p< 0.05). No significant differences in HOOS subscores between subjects of group 1 and 2 for subsequent time points were found. The scores related to Pain and Symptoms increased significantly 6 weeks after THR (p< 0.01). Sports and recreation scores increased significantly up to 3 months after THR (p< 0.01). Activities of daily living, and Quality of Life (QoL) improved up to 6 months after surgery (p< 0.01).

No significant difference between the 2 groups in QoL was observed. The physical component summary increased up to 3 months after surgery (p< 0.01). The mental component summary did not change significantly after THR.

The difference noted in HHS between group 1 and 2 may be due to the selection of the fixation technique which is often directly related to the patient’s age. The results of the HOOS score confirm the findings of the HHS. Not all patients responded to the questions relative to recreation and sport of the HOOS score. QoL is an important indicator for success as perceived by the patient. In this study a rapid improvement of QoL is observed (3 months) and there is little change at 6 and 12 months.

Success of a total hip replacement is commonly assessed by the Haris Hip Score (HHS), which provides information on pain reduction and regained mobility. Radiographic images provide information relative to the stability of the prosthesis.

We use the intraoperatively manufactured prosthesis since 1989; the initially performed THR were done with uncoated prostheses. After introduction of the hydroxyapatite coating our prosthesis stems were coated.

We retrospectively evaluated the clinical and radiographic outcome of 3 patient cohorts who received intra-operatively custom made stem prosthesis.

Group 1: Uncoated stem prosthesis fixated with tro-chanteric osteotomy.

Clinical assessment and radiographic assessment is performed using pre-operatively and at each follow-up visit.

Baseline data are the pre-operative HHS and first radiography postoperatively. These data are compared with the data of the latest follow-up visit.

RX’s are scored according to the ARA score.

Records were analysed for 83 patients in group 1, with a mean follow-up period of 93 months. In group 2, 35 patients were followed for 105 months and 54 patients from group 3 were followed for 41 months.

In the 3 groups the HHS at follow-up was > 75, this means an improvement of minimum 25 points for group 1 and 2 (baseline HHS for group 2 was not available)

The mean ARA scores at follow-up were 1.6; 1.7 and 5.3 for respectively group 1; 2 and 3.

Clinical outcome is comparable in the three studied cohorts.

The ARA score is indicating poor outcome for the uncoated prosthesis, regardless of the type of fixation, while the coated prosthesis group has a good to excellent ARA score.

These findings tend to confirm the superiority of the hydroxyapatite coated prosthesis.