Purpose of the study: Radiographs of 24 patients who underwent surgery for total hip arthroplasty (THA) with a locked stem were reviewed at 38 months mean follow-up using a dedicated software. This software enables digital analysis of standard radiographs with semiquantitative evaluation of bone density.

Material and method: Good quality postoperative AP views of the femur and the same view at last follow-up were selected using the same criteria. These images were digitalised then analyses with the software. Bone density was established along a horizontal line 1 cm below the lesser trochanter perpendicular to the femur shaft. Computer analysis of bone density established three categories of patients as a function of cortical density: no cortical modification (n=5 hips), modification of only one cortical (n=11) and modification of both corticals (n=8).

Results: Bone density increased, suggesting improve cortical bone stock as has been reported by most authors using the transfemoral approach and a non-cemented locked stem.

Discussion: This result confirms the data in the literature; data which, unlike our series, were established on qualitative or subjective evaluations. The method presented here has the advantage of a semi-quantitative analysis, simple use, applicable to plain x-rays, and good reproducibility since all measures are made by the software. This study demonstrated the notion of cortical quality since it was not limited to a simple measurement of width, but also bone density, closer to real intraoperative observations.

Conclusion: Use of this method enables longitudinal study to establish the kinetics of bone remodelling, compare results between surgical methods, and search for factors explaining observed variations.

Purpose of the study: Navigated surgery for implantation of knee prostheses has demonstrated pertinence in terms of quality and regularity of the implantation. This technique requires insertion of rigid position captors in the bone during the operation. We report a series of five femoral fractures which occurred on the pin tracts in a consecutive series of 385 patients and analyse the causes and means of prevention.

Material and methods: This was a retrospective clinical and radiographic analysis of five patients among our consecutive series of 385 patients, who suffered fractures on navigation pin tracts.

Results: There were five femoral fractures, in four women and one man, mean age 73.2 years (65–79). The mean body mass index was 32.56 (24.15–39.45). The rate of this complication was 1.3%. The fractures occurred on average 12.6 weeks (range 7–21) after implantation of the prosthesis. The fractures were always preceded by thigh pain and occurred in a context of minor or indirect trauma. The fracture lines always started from a pin tract orifice. In four of five cases, the pins had been inserted in a diaphyseal zone and at least one was in a transcortical position. The five fractures healed with no functional sequel at last follow-up after osteosynthesis with a nail or plate and no complementary bone graft.

Discussion: The incidence of these fractures on navigation pin tracts is estimated at 1.3%. Surgeons must be aware of this complication and describe the risk to patients. These fractures occur late after the implantation, in obese patients, after an episode of thigh pain. Treatment requires stable osteosynthesis but does not compromise the knee prosthesis. These fractures are favoured by low and transcortical diaphyseal position of navigation pins. Prevention requires implantation of bicortical metaphyseal navigation pins. The development of pain in the thigh late after a knee prosthesis implantation, in a favouring context (obese patient, low diaphyseal pin orifice, transcortical tract) should suggest possible fracture requiring complete rest.

Which parameters are related with a forgotten knee after TKA?

The operated knee was said forgotten when it was similar to the normal controlateral knee in all situations.

When a restriction existed, the knee was considered as not forgotten.

470 patients operated with a stabilised mobile bearing knee were examined with a minimal follow up of 5 years and answered to this question.

4 groups of parameters: patient, prosthesis, surgery and post operative care were compared to the binary answer to the forgotten knee question.

48% of the patients had a forgotten knee one year after the TKA;

The following factors had a significant negative correlation with the forgotten knee:

low SF12 psychological profile; Patellofemoral dysplasic arthritis (p = 0,01);

We found no correlation between the following factors and the forgotten knees:

gender, BMI, approach, cemented or not, patellar resurfacing; preoperative Oxford and Knee Society knee scores;

The forgotten knee is a simple objective clinical item because the answer to the question is binary and does not accept any unprecision. It is highly correlated with surgical scores and patients expectation scores (p = 0,0001).

The forgotten knee is a painless and asymptomatic knee identical to a normal knee.

Surgical factors have the highest infiuence on this parameter compared to patient or prosthetic related factors.