Small and similar amounts of micromotion in an anatomical stem and a customized cementless femoral stem in regular-shaped femurs: A 5-year follow-up randomized RSA study

Background and purpose

High primary stability is important for long-term survival of uncemented femoral stems. Different stem designs are currently in use. The ABG-I is a well-documented anatomical stem with a press-fit design. The Unique stem is designed for a tight customized fit to the cortical bone of the upper femur. This implant was initially developed for patients with abnormal anatomy, but the concept can also be used in patients with normal femoral anatomy. We present 5-year radiostereometric analysis (RSA) results from a randomized study comparing the ABG-I anatomical stem with the Unique femoral stem.

Patients and methods

100 hips with regular upper femur anatomy were randomized to either the ABG-I stem or the Unique femoral stem. RSA measurements were performed postoperatively and after 3, 6, 12, 24, and 60 months.

Results

RSA measurements from 80 hips were available for analysis at the 5-year follow-up. Small amounts of movement were observed for both stems, with no statistically significant differences between the 2 types.

Interpretation

No improvement in long-term stability was found from using a customized stem design. However, no patients with abnormal geometry of the upper femur were included in this study.High mechanical stability is a crucial factor for correct performance of uncemented femoral stems. Micromovements along the implant-bone interface may prevent ingrowth of bone to the surface of the prosthesis, and it may lead to the formation of a fibrous membrane and eventually to loosening of the implant. The critical thresholds of micromovements that can be tolerated are not exactly known, but they are probably dependent on both patient- and implant-specific factors (Viceconti et al. 2006). It has been shown, however, that interfacial motion of around 40 μm leads to partial bone ingrowth whereas motions exceeding 150 μm completely prevent ingrowth of bone (Pilliar et al. 1986, Jasty et al. 1997).Uncemented, customized femoral stems are mainly designed and manufactured for patients with abnormal size and shape of the proximal femur, but this does not preclude their use in patients with regular-shaped proximal femurs. The requirement for maximum primary stability with uncemented off-the-shelf stems also applies to customized stems. The optimized fit and fill of a customized stem should theoretically promote even better mechanical fixation than with standard implants.Radiostereometric analysis (RSA) enables measurement of migration and rotation in the range of 0.1 mm and 0.05º, respectively (Selvik 1989, Kadar et al. 2011). There is a correlation between postoperative migration of femoral stems and early loosening (Freeman and Plante-Bordeneuve 1994, Linder 1994, Karrholm et al. 2006, Karrholm 2012). On the other hand, a new implant showing large degrees of micromovement should not necessarily be regarded as having a performance equivalent to long-term failure (Karrholm et al. 2006). Recently published studies reporting medium- to long-term RSA results will probably contribute to a better understanding of the topic (Nieuwenhuijse et al. 2012, Rohrl et al. 2012).This randomized study was performed as part of the clinical documentation of the Unique customized stem (Scandinavian Customized Prosthesis (SCP), Trondheim, Norway), to compare the migration pattern of the Unique stem with that of a standard anatomical uncemented stem with a clinically well-proven stem design (the ABG-I).Our aim was to measure migration of the Unique customized stem and the ABG-I stem using RSA. Our hypothesis was that there would be no difference in migration between the 2 types of uncemented femoral stems in patients with regular anatomy in the upper femur.     

Combined cilioretinal artery and hemi-retinal vein occlusion in Sturge Weber syndrome: Expanding the clinical spectrum

A 9-year-old boy with the diagnosis of Sturge-Weber Syndrome, and port-wine stain involving the right side of the face, presented with acute visual loss of the right eye. Examination revealed a high intraocular pressure and a combined cilioretinal artery and inferior hemi-retinal vein occlusion in the right eye. Systemic work-up was negative. After controlling the intraocular pressure, gradual improvement of vision was noticed with simultaneous disappearance of signs of vascular occlusion.     

Pelvic rotations: a pelvic phantom study

Background: Radiographic measurements made on standard pelvic radiographs are commonly used in studying conditions related to the hip joints. Effects caused by variations in pelvic orientation may be a source of error in comparing measurements between sequential radiographs.

Purpose: To define and characterize parameters able to measure rotational differences separately around two axes and altered radiographic focusing along two axes when sequential standard anteroposterior (AP) pelvic radiographs are compared.

Material and Methods: A pelvic phantom was constructed based on direct three-dimensional measurements of five defined landmarks in a pelvic model. Two ratios, the vertical and transversal rotation ratios, were defined using radiographs of the phantom. The phantom was radiographed in 33 different orientations and with 16 different radiographic focuses using a specially constructed tilt table. On each radiograph, measurements were made and the two rotation ratios were calculated using a measurement program.

Results: Linear correlations between pelvic rotations around one axis and the corresponding rotation ratio were found with almost no influence of simultaneous rotation around the other axis. Also, linear correlations were found between altered radiographic focusing along one axis and the non-corresponding rotation ratio.

Conclusion: Rotational differences around two axes or altered radiographic focusing along two axes can be measured independently. Effects caused by rotations cannot be distinguished from effects caused by altered radiographic focusing.     

Survival analysis of recurrent squamous cell carcinoma of the lower oral cavity treated by surgery

The aim of the present study was to investigate the survival of individuals with squamous cell carcinoma of the lower oral cavity who underwent surgical treatment and experienced recurrence, considering the site of the recurrent disease. A retrospective longitudinal study was conducted, comparing the survival rates of patients with and without recurrence and considering the site of recurrence (local, regional, distant). Statistical analysis was performed with SPSS and a p-value ≤ 0.05 was considered significant. The sample comprised 150 patients, 59 (39.3%) of whom experienced recurrence. Local recurrence occurred in 35 patients (23.4%), regional recurrence in 17 (11.3%), and distant recurrence in seven (4.6%). The average survival of participants with local, regional, and distant recurrence was 12, five, and two months, respectively. Patients with recurrent disease had worse survival than those who did not (P < 0.001). Patients with local recurrence had better survival than those with regional/distant recurrence (P = 0.011). All patients with regional and distant recurrence had deceased by the last follow-up. In conclusion, patients with local recurrence of squamous cell carcinoma of the lower oral cavity treated by surgery have a better survival rate than those with regional and distant recurrence. Local recurrence poses the possibility of curative salvage therapy.     

The effect of interlocking parallel screws in subcapital femoral-neck fracture fixation: a cadaver study

Background

A new locking-plate for femoral-neck fractures that provides angular stability to three screws in an inverted triangle configuration was evaluated. The plate is not fixed to the lateral cortex and therefore represents a new treatment principle.

Methods

Twelve pairs of cadaver femurs (mean T-score − 1,95 (range − 4,5–0)) with subcapital femoral-neck fractures angulating 60° were randomly allocated to fracture-fixation using either three individual screws or three interlocked screws. Subject-specific axial force and torque were applied by a hip simulator and three-dimensional migrations were recorded. The femurs underwent 10,000 cycles of simulated partial weight-bearing, followed by 10,000 cycles of simulated full weight-bearing and stair climbing.

Findings

On average interlocking reduced femoral-head centre migrations 1.6 mm (95% CI 0.1–3.1, P = 0.04). The intra-pair correlation of migration was 0.953 (Pearson's r). Interlocking did not change rotational stability (P = 0.87). Adding a locking plate did not affect the risk of failure, however all failed femurs were fixed using the smallest-sized aiming guide.

Interpretations

Adding a lateral interlocking plate to three screws might improve the fracture stability. However, none of the implants were able to resist the unwanted deformation of the proximal femur. Regardless of the fixation, female sex, reduced bone quality and small sized femurs appear to increase risk of failure.     

The usefulness of a pectoralis major myocutaneous flap in preventing salivary fistulae after salvage total laryngectomy

Salvage laryngectomy in patients treated with organ preservation protocols is associated with high rates of postoperative complications. The use of non-irradiated tissue flaps in pharyngeal reconstruction could reduce the incidence of these complications.Objective: This study aims to evaluate the usefulness of the pectoralis major myocutaneous flap in preventing salivary fistulae during the postoperative period of salvage total laryngectomy (TL).Materials and Method: This retrospective study enrolled 31 patients operated between April of 2006 and May of 2011. All patients had advanced cancer at the time of the salvage procedure and had been treated with chemoradiotherapy or radiotherapy alone. Pharyngeal reconstruction was performed using pectoralis major myocutaneous flap in 19 cases (61%); primary wound closure occurred in 12 patients (39%).Results: Salivary fistulae occurred in 16% of the patients who received the flap and in 58% of the patients with primary closure of the pharynx (p < 0.02). No statistically significant differences were noted between the groups with respect to the mean time for fistula formation, reintroduction of an oral diet, or use of a nasoenteric tube for feeding.Conclusion: The pectoralis major myocutaneous flap was found to reduce the incidence of salivary fistulae in salvage laryngectomy procedures.     

The rotation ratios method: a method to describe altered pelvic orientation in sequential radiographs

Background: A method to describe pelvic rotations between pairs of standard sequential pelvic anteroposterior radiographs based on a pelvic phantom is described in a former study.

Purpose: To expand this method into clinical use based on clinical data.

Material and Methods: Teardrop distances were measured on 262 pelvic radiographs from 46 patients in a clinical material using a computer program designed to perform measurements on digital radiographs. Anthropometric data recorded from 141 pelvises in an anatomical collection were employed in a computer program designed to simulate radiographs of virtual objects. Virtual rotations of the pelvises were carried out with 4653 virtual radiographs obtained. Virtual radiographic measures were analyzed.

Results: A statistically significant difference of 8 mm between mean teardrop distance in females (120 mm) and males (112 mm) was found in the clinical material. A set of formulas describing the relations between differences of two rotation ratios and pelvic rotations were derived. Four simple regression analyses were carried out with the use of virtual measures. Adjusted teardrop distances were implemented.

Conclusion: A clinical method to describe pelvic rotations using standard pelvic radiographs was developed.     

Periprosthetic bone loss after insertion of an uncemented, customized femoral stem and an uncemented anatomical stem. A randomized DXA study with 5-year follow-up

Background and purpose

Customized femoral stems are designed to have a perfect fit and fill in the femur in order to achieve physiological load transfer and minimize stress shielding. Dual-energy X-ray absorptiometry (DXA) is regarded as an accurate method for detection of small alterations in bone mineral density (BMD) around hip prostheses. We present medium-term DXA results from a randomized study comparing a customized and an anatomical femoral stem.

Methods

100 hips were randomized to receive either the anatomical ABG-I stem or the Unique customized femoral stem, both uncemented. DXA measurements were conducted postoperatively and after 3, 6, 12, 24, 36, and 60 months, and BMD was computed for each of the 7 Gruen zones in the proximal femur.

Results

Results from 87 patients were available for analysis. 78 completed the 5-year follow-up: 35 patients in the ABG group and 43 patients in the Unique group. In both groups, we found the greatest degree of bone loss in the proximal Gruen zones. In zone 1, there was 15% reduction in BMD in the ABG-I group and 14% reduction in the Unique group. In zone 7, the reduction was 28% in the ABG-I group and 27% in the Unique group. The only statistically significant difference between the groups was found in Gruen zone 4, which is distal to the tip of the stem, with 1.6% reduction in BMD in the ABG-I group and 9.7% reduction in the Unique group (p = 0.003).

Interpretation

5-year DXA results showed that because of stress-shielding, proximal bone loss could not be avoided—either for the anatomical ABG-I stem or for the customized Unique stem.Implantation of a prosthesis in the femur alters the load distribution in the host bone, and the femur remodels to adapt to the new mechanical situation (Engh and Bobyn 1988, Bobyn et al. 1992, Engh et al. 1999). A perfect fit and fill in the proximal femur is said to be important to achieve physiological load transfer (Laine et al. 2000). It has therefore been hypothesized that a customized femoral stem could fulfill the criterion for optimal fit and fill, and thus minimize stress shielding in the proximal femur (Bargar 1989). Based on numerical analyses, however, it has been claimed that canal-filling femoral stems may cause stress shielding and subsequently bone atrophy of the proximal femur (Huiskes et al. 1989).In vitro studies on human cadaver femurs have indicated that insertion of a customized stem gives a better pattern and distribution of cortical strains in the proximal femur than anatomical stems (Aamodt et al. 2001, Østbyhaug et al. 2009). In these studies, it was shown that 33–56% of the external cortical strains were retained on the proximal, medial aspect of the femur after insertion of a customized stem whereas the corresponding figure was 10–13% after insertion of a standard, anatomical stem. Long-term bone remodeling is, however, not necessarily reflected in the immediate postoperative mechanical situation in the femur as measured in experimental strain analyses.The present randomized, clinical study was undertaken to compare (by DXA) the medium-term changes in bone mineral density in the proximal femur after insertion of an uncemented, customized femoral stem and an uncemented, standard anatomical femoral stem.