Aims

There is little information in the literature about the use of dual-mobility (DM) bearings in preventing re-dislocation in revision total hip arthroplasty (THA). The aim of this study was to compare the use of DM bearings, standard bearings, and constrained liners in revision THA for recurrent dislocation, and to identify risk factors for re-dislocation.

Dual-mobility (DM) bearings are effective to mitigate dislocation in revision total hip arthroplasty (THA). However, data on its use for treating dislocation is scarce. Aim of this study was to compare DM bearings, standard bearings and constrained liner (CL) in revision THA for recurrent dislocation and to identify risk factors for re-dislocation.

We reviewed 100 consecutive revision THAs performed for dislocation from 2012 and 2019. 45 hips (45%) received a DM construct, while 44 hips (44%) and 11 hips (11%) had a standard bearing and CL, respectively. Rates of re-dislocation, re-revision for dislocation and overall re-revision were compared. Radiographs were assessed for cup positioning, restoration of centre of rotation, leg length and offset. Risk factors for re-dislocation were determined by cox regression analysis. Modified Harris hip scores (mHHS) were calculated. Mean follow-up was 53 months (1 to 103).

DM constructs were used more frequently in elderly patients (p=0.011) and hips with abductor deficiency (p< 0.001). The re-dislocation rate was 11.1% for DM bearings compared with 15.9% for standard bearings and 18.2% for CL (p=0.732). Revision-free survival for DM constructs was 83% (95% CI 0.77 – 0.90) compared to 75% (95% CI 0.68 – 0.82) for standard articulations and 71% (95% CI 0.56 – 0.85) for CL (p=0.455). Younger age (HR 0.91; p=0.020), lower comorbidity (HR 0.42; p=0.031), smaller heads (HR 0.80; p=0.041) and cup retention (HR 8.23; p=0.022) were associated with re-dislocation. Radiological analysis did not reveal a relationship between restoration of hip geometry and re-dislocation. mHHS significantly improved from 43.8 points to 65.7 points (p<0.001) with no differences among bearing types.

Our findings suggest that DM bearings do not sufficiently prevent dislocation in revision THA for recurrent dislocation. Reconstruction of the abductor complex may play a key role to reduce the burden in these high-risk patients.

Study Purpose

To examine the presence of radicular pain and its relationship to the degree of lumbar nerve root compression in patients with a degenerative lumbar spine condition about to undergo surgery for either lumbar disc prolapse or lumbar canal stenosis.

The last years showed an increasing demand especially of younger patients for bone protecting total hip arthroplasty. Apart from the well known cemented versions a cementless implant with a variable short stem has been developed. It also consists on a metal backed metal inlay.

The femoral component of the Eska Hip Resurfacing System is surfaced on the bone side with the well experienced metal-spongiosa II three dimensional structure. The femoral component can be combined with a short stem either of 30 or 50 mm of length. The diameter increases in two millimeter steps. The socket component is also covered with the metal-spongiosa II structure. The cup inlay is secured by conical fixation and can be changed.

We think the implant offers a very helpful new development in the cementless hip resurfacing arthroplasty. First technical problems have been solved.

Friction was studied in 67 retrieved cemented cups with 32 mm internal diameter. Friction was measured under 1.0 KN of static load. High molecular hyaluronic acid was adapted as a lubricant. Thirty cups were combined with alumina heads and 37 were combined with metal heads. The years cups were in situ was 7.5 (3.2–13.2) for alumina-polyethylene implants and 8.9 (1.5–15.7) for metal-polyethylene implants (p> 0.05).

The revision rate at 15 years follow-up was higher in metal-polyethylene (PE) implants (57%) than that of alumina-PE implants (40%) (p< 0.05). The prevalence of cup loosening was less in alumina-PE implants (12/30) than in metal-PE implants (29/37) (p< 0.01). Less wear was observed in alumina-PE implants (1.15+−0,80mm) than in metal-PE implants (1.62+−0.61mm) (p< 0.01). Less wear was observed in cups without loosening (alumina-PE implants: 1.84+−0.57mm, metal-PE implants: 1.75+−0.51mm) than in those with loosening (alumina-PE implants: 0.69+−0.56mm, metal-PE implants: 1.31+−0.73mm) in both types (alumina-PE implants: p< 0.01, metal-PE implants: p< 0.05). Less wear rate was observed in cups without loosening (alumina-PE implants: 0.11+−0.05 mm/year, metal-PE implants: 0.14+−0.05mm/year) than in those with loosening (alumina-PE implants: 0.17+−0.03 mm/year, metal-PE implants: 0.22+−0.09mm/year) in both types (alumina-PE implants: p< 0.01, metal-PE implants: p< 0.05). The coefficient of friction increased in proportion to the progress of cup wear in both types (alumina-PE implants: r2 =0.217, p< 0.01, metal-PE implants: r2 =0.183, p< 0.01). Relation between the coefficient of friction and stability of implants was not detected in both types, while alumina-PE implants had lower coefficient of friction (0.137+-0.056) than metal-PE implants (0.209+−0.098) (p< 0.01). The torque of metal-PE implants without stem loosening (0.137+−0.053) was larger than that of alumina-PE implants with stem loosening (0.274+−0.088) (p< 0.01).

The results suggest that wear has greater influence on stability of implants than the friction, whereas coefficient of friction increases in worn implants.

A method was developed to take radiographs showing the inner articulation of bipolar hip prostheses. By this method, wear was measured in 68 hips whose inner head diameter was 22 mm. Average annual wear rate was 0.17 mm. Osteolysis was observed in 25 hips (37%) and there was no difference between the annual wear rate of hips with and without osteolysis. Studying 19 retrieved prostheses, abrasion of the rim was deeper in hips with osteolysis than those without it. Wear rate of the inner articulation in bipolar hip prosthesis is much larger than that in Charnley’s prosthesis, as linear penetration into the articulation surface reduces the motion range of the inner articulation and this increases impingement and advances rim abrasion.

Introduction: Modern navigation technology appears to be acquiring an established place in the fields of total knee arthroplasty. This technology helps the surgeon to apply his manual skills with greater precision and thus more effectively, and its positive impact on the quality of surgical treatment has already been demonstrated. The Surgetics navigation system described in this paper shows that the Technology can be adapted to the requirements of daily surgical practice, without compromising its utility to the surgeon.

The Surgetics navigation system: The Surgetics navigation system represents a multifunctional tool, that can be used in a lot of fields in orthopedic surgery. For every special use as prosthesis, osteotomies ore ACL-replacement, the hard- and software is adapted thus not any compromise should be accepted for the surgical procedure. In total knee prostheses navigation no ct- scan is needed preoperatively, the patented bone morphing procedure is entering all the anatomic datas to the computer for an absolutely correct positioning of the implant. Consequently the pre- and intraoperative inputs are reduced to a minimum.

Material: To evaluate the advantage of the Surgetics navigation system in total knee prosthesis, the technical datas of a non constrained knee prostheses with rotational platform (ESKA) had been entered in the system. The patient datas, concerning size of the knee joint, leg axes, center of rotation of the hip joint and ligament balance are transmitted by rigid bodies and a pointer with 6 reflecting markers each and a stereo infrared camera. The rigid bodies are fixed by two thin Steinmann-nails each in the tibial and femoral bone. On a monitor each step of the bone morphing and the surgical procedure is shown. Thus the bonecutting guides are placed in an absolutely correct position. The extension – and the flexion gap is presented as well for a precise ligament balancing. The additional time for using this system is not extending 15 minutes.

Methods: 50 ESKA total knee prosthesis with rotational platform have been implanted with standard instrumentation and another 50 with the use of the Surgetics navigation system. In both groups the reason fore surgery has been nearly identic. In 92% the patients suffered from arthritis. More varus than valgus deformities have been seen. The range of deformity went up to 25 degrees.In 8% posttraumatic deformities with consecutive arthritis leaded to surgery. Preoperative X rays of the whole leg in a standing position have been taken, the shifting of the bearing axes in comparison to the center of the knee joint has been determined. The maximum of this shifting was 6.3 cm. The HSS score has been used to describe the clinical findings pre- and postoperativly. In 38 cases of the S- group and in 39 of the N- group the joint was inserted cementless. 2 in the s-group and 1 in the n-group in a hybrid technic, the rest cemented.

Results: The follow up time in both groups ranged from 6 month to one year.Because it has not been the purpose of this paper to report on long time clinical results or survivership, this short follow up time seems to be acceptable for the evidence upon the value of a navigation system.The postoperative x- rays showed a correction of the bearing axes of the leg in relation to the center of the knee joint in a 4 degree corridor in 94,6% for the N – group and in 69,9% in the S- group. Two failures in the N-group came from a change of position of the rigid bodies during surgery due to pushing them by lack of caution.

Conclusion: The surgetics navigation system is a technical help for the orthopedic surgeon, improving the radiological and clinical results in knee arthroplasty. The correction of the bearing axes in the 4 degree corridor is significantly higher in the N-group then in S-group. This has as well an important influence on the clinical outcome. The HSS score by first impression differs by 6 points. The use of the system is economically reasonable,because preoperative ct- scan is not needed and the time of surgery is not extended more than 15 minutes.The Surgetics navigation system with its sophisticated software is leading the surgeon visually through the bone morphing procedure, the bone cutting process and the ligament balancing step by step.

For younger patients many surgeons recommend femoral neck endoprostheses as alternative to stemmed implants in THA. Due to metaphyseal anchorage several advantages are quoted, e.g. preservation of the femoral diaphysis for a revision implant. Determinant factor for long-term implant stability is the load transmission to the bone. Because so far only few information about the load transfer of femoral neck endoprostheses exist, a photoelastic analysis was performed. Aim of the study was the comparison of bony strain pattern before and after implantation of a femoral neck endoprosthesis.

‘Composite-femurs’ (Pacific Research Labs) were used due to of their mechanical characteristics close to human femurs but better reproducibility. Three femurs were coated with photoelastic material. The femurs were loaded prior and post implantation of a femoral neck endoprosthesis type Cigar (ESKA Implants). Test load consisted of the resulting hip joint force and muscle forces (abductors, tractus iliotibialis). Load was applied statically by a universal testing machine and additional weights. Bony strain was measured along the medial, ventral, lateral and dorsal cortex. Statistical analysis of the implant related strain alterations was based on a 99% confidence interval.

The unresected femurs showed an excellent match of bony strain patterns. Implantation of femoral neck endoprostheses caused highly significant strain changes at the trochanteric region. Greatest differences were observed at the lateral cortex. Above the implant’s traction screw former areas of tension changed to compression. Along the medial cortex below the resection plane strain reductions were measured but disappeared at the latest at 40 mm below. No significant changes in strain were detected at the ventral and dorsal cortex.

Implant related bony strain alterations were limited to the trochanteric region of the femur. A marked strain alteration at the lateral trochanteric aspect was measured. Whether this is of clinical importance can not be answered yet.