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.

Radiostereometric analysis (RSA) is a technique that can be used to measure in-vivo micro-motion of the components of hip arthroplasty.

86 patients received a titanium custom-made prosthesis. The average age was 64 year (20y –84y). During the study 30 patients out of 86 received a cementless femoral stem. The choice of stem fixation is determined by the quality of the bone. In all cases a 36 mm cobalt chromium head is used. Spherical tantalum markers, chosen because of the proven biocompatibility, were inserted into stable locations in the femoral bone during surgery using a specialized insertion tool, according to the protocol. Evaluation was done 1, 6, 12, 24, 52 weeks after surgery.

Overall subsidence follows a parallel pattern for the cemented and uncemented prosthesis that is slightly stronger in for the uncemented prosthesis. Over the 6 months evaluation period the prosthesis migrates towards the lateral side with 0.25 mm in both groups. An anteroversion of 0.5° to 1° is noted at 6 months follow-up. The varus valgus movement of the prosthesis is similar for both groups at 6 months. At 6 weeks a slight valgus flexion is noted, this is reversed at 3 months. At this point in time the effect is more pronounced in the group with a cemented prosthesis.

Micro motion is difficult to assess on plain radiography. In this study more subsidence is noted in the uncemented prosthesis compared to the cemented. The degree of rotation of the stem measured in our study is comparable with those reported by others. In our primary THR we observe a bi-modal micromotion except for the subsidence the initial movement up till 6 weeks is reversed at 3 months follow-up and at 6 months the prosthesis seems stabilized, though longer follow-up is required to confirm stabilization.

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.