Modular hip designs offer potential for customising the implant to the patient. However, the more features a device has to offer, the potential for misuse increases. This paper will review one modular stem and the pearls learned over the years to make this a simple and reproducible surgical technique.

Over a 1,000 primary THA have been performed since the development of the proximal modular stem in 2000. The two senior surgeons developed the stem design and surgical techniques used and described here. Two additional surgeon co-authors have used the device as described confirming the design and techniques to be simple, reliable and reproducible.

Often the tricks of the trade go unpublished and each new surgeon is left to his own learning curve with new devices. As with any surgical instrumentation there are significant little techniques that often make surgery more reproducible and enjoyable.

Surgical technique should be simple and reproducible. We have found that even simple procedures—such as head resection—can, and do, impact the surgical process and can affect surgical outcome. Canal reaming, flute engagement, conical reaming, broaching, trochanter clearance, proper use of modular trials and implant assembly all play critical roles to a successful outcome.

We have found, and previously reported, that the use of this proximal modular stem design has reduced our leg length inequalities +/− 5 mm and has all but eliminated dislocations and aseptic loosening.

There were some mechanical failure problems (previously reported) on the first generation modular junction design that was identified and corrected (never exported outside the U.S.). There have been no reported failures since introduction of the improved modular junction six years ago.

Independent selection of femoral offset and vertical height is possible and we feel that restoration of joint mechanics is more reproducible with proximal modular devices as compared to monoblock stems. It is the responsibility of surgeons to communicate their understanding and experience with newer devices and not rely on industry to fill this function.

Hip simulator studies on MOM bearings have historically involved ‘custom’ cetabular cups. I.e. having neither beaded layers nor biological coatings.

The aim of this study was to investigate wear using such MOM bearings and evaluate the potential wear and evaluate the potential for error in the gravimetric assessment.

Six x 38 mm HC Co-Cr bearings were supplied (Global and IO International Orthopaedics). The cups were received in ‘off-the-shelf’ condition with a cast Co-Cr beaded/HA-coated backing. To remove the HA-coating, the cups were pre-soaked in lemon juice for 4 days (articular surfaces shielded). Custom plastic fixtures were machined to fit the beaded contours of the cups. Test duration was 5Mc inorbital hip simulator (Shore-Western). MOM wear was estimated from serum ion contamination. Serum samples were digested and assessed using ICP/MS (Weck Labs Inc, CA).

The majority of the HA-coating was removed from the cups after four days of soaking inlemon juice after 21 days of soaking all cup weights appeared atable (within 1 mg). Reflected-light microscopy (RLM) showed no descernible signs of HA and the total weight loss due to HA remval averaged∼400mg.

During hip simulator there was no visual evidence of lost or broken beads, 3rd body abrasion etc (Sa<30nm). Both gravimetric and metal ion analysis showed consistent wear trends for all MOM cups. The MOM with the highest wear (predicted by ion analysis) demonstrated 1.2 mm (3)/Mc)OWR) at 5Mc. In comparsion, gravimetric analysis predicted an OWR of 1.3 mm (3)Mc for the same MOM, a difference of only 8%. Soaking beaded-HA cups in lemon juice and BCS proved effective in removing the coating.

The beaded cups remained stable in weight during the wear study and caused little discrepancy in gravimetric analysis (8%).

The method described did not lead to breaking of beads, elevated 3rd-body abrasion, cup damage or distorted wear scars.

Introduction: Architectural changes in the proximal femur after THA continue to be a problem. In an attempted, to reduce these changes some surgeon designers have advocated the concept of neck sparing stem designs.

To-date neck-sparing stems have been disappointing in their ability to maintain the calcar. A new approach was undertaken to improve load transfer and to create a tissue-sparing stem that would be simple in design, reproducible in technique and provide for fine-tuning joint mechanics while maintaining compressive loads to the calcar.

Methods: Review of previous published work was evaluated along with FEA modeling in creating a new approach to neck sparing stems for THA. The MSA^™ Stem is a simple curved stem with a unique lateral T-back designed for torsional stability, ease of preparation and insertion. The proximal design has a novel proximal conical shape designed to transfer compressive forces to the calcar.

A modular neck provides for fine-tuning joint mechanics.

Results: FEA modeling will be reviewed. Strain patterns for the MSA^™ stem demonstrated better patterns vs. long stems or the short Biodynamic stem.

Discussion: In theory neck retaining devices provide or:

Bone and Tissue sparring

We are encouraged and believe there are advantages in the concept of neck sparing stems. Clinical/surgical evaluation is now underway and will be reported on in the future.

Cemented total knee arthroplasty has excellent long term survivorship however deficiencies of the cement mantle can compromise results. Minimising mantle deficiencies and increasing mantle size, may improve implant fixation and survivorship. The aim of this study was to evaluate the effectiveness of pressurized carbon dioxide lavage in an attempt to increase cement penetration into bone.

Two consecutive series of TKAs where performed by the senior surgeon. During the first series standard cementing techniques where utilised prior to prosthesis implantation. The bone surfaces were cleaned with pulsatile lavage and then dried prior to cementation (n=69). During the second series a jet of high pressure carbon dioxide was also delivered to the bone surfaces via a hand held device (CarboJet, Kinamed Inc, Global Orthopaedic Technology)(n=50). A single investigator reviewed standardised post operative radiographs with respect to, depth of cement mantle around the prosthesis, and the presence of mantle defects.

The cement mantle around the tibial and femoral prosthesis was divided into multiple zones, similar to that applied by the Knee Society. The depth of cement penetration was then measured for each zone in 0.5 mm increments using a 115% rule. Depths were averaged and then analysed using students’ T test. Cement penetration was greater with the use of pressurized carbon dioxide lavage. The greatest difference was seen in zones 1 and 4 beneath the Tibial prosthesis. A Significant difference was noted between groups.

The size of the cement mantle can be increased with the use of pressurized carbon dioxide lavage. It is postulated that the bone interstices are cleared of fat and fluid more effectively than with fluid lavage alone. This may lead to an improved outcome for cemented total knee arthroplasty.

Background: A totally new double-threaded cone-shaped modular femoral stem has been designed, using rotational rather than percussive hammer insertion of the prosthesis. The vertical height, the neck length, the neck anteversion angle and the medial offset can all be adjusted after preparation of the femoral canal has been completed.

Methods: The new stem design and the technique of insertion are described. A consecutive series of the first 110 hip joints in 103 patients were followed clinically and radiographically for an average of 28 months.

Results: The Harris hip score average rose from 43.6 points preoperatively to 91 points postoperatively. The pain score average changed from 7.9 points to 42 points, respectively. Thirteen hips (11.8%) had mid-thigh pain, most of them mild. One hip (0.9%) showed clinical and radiographic signs of early loosening and was revised.

Conclusions: The short-term clinical and radiographic outcomes were encouraging. The double-threaded cone-shaped stem locking mechanism was shown to be able to withstand the torsional and vertical forces applied to a hip-replacement prosthesis.

Introduction: The double threaded Cone Modular Hip Replacement System has been used in 114 patients as a primary prosthesis in over three years. No patient has been lost to follow up and all patients have been assessed postoperatively for the Harris Hip Score, Pain Score, Dexa analysis as well as plain X-rays.

Method: 114 patients requiring primary hip replacement were entered into a prospective clinical trial over a three year period. The Harris Hip Score, Pain Score and Dexa analysis (Luna 2000 program) and X-rays were assessed at six weeks, three months, six months, twelve months, two years and three years and results were compared with the preoperative figures. Length of hospital stay, discharge details (home or rehabilitation unit) and physiotherapy assessment of time to independent stair climbing was prospectively assessed.

Results: The Dexa analysis indicates a loss of bone at two years at Gruen’s zones one and seven of 25% and at zones two and six of approximately 20% with no increase or loss of bone in zones three, four and five.

The Harris Hip Scores and Pain Scores show a significant improvement comparing preoperative with postoperative results in this series.

One patient required revision of the femoral neck component for recurrent dislocation and three patients have significant rotational thigh pain due to varus implantation of the stem (the pilot has since been shortened and the diameter reduced by 1mm).

Conclusion: The double threaded cone shaped modular hip prosthesis stem allows immediate full weight bearing postoperatively. No prosthesis has loosened or subsided and the locking mechanism has been shown to gain immediate and long term fixation as a primary prosthesis stem.

Clinical assessment, X-rays and Dexa analysis indicate satisfactory results with good incorporation of the prosthesis by the bone.

Background: A total new double-threaded cone-shaped modular femoral stem has been designed, using rotational rather than percussive hammer insertion of the prosthesis. The vertical height, the neck length, the neck anteversion angle and the medial offset can all be adjusted after preparation of the femoral canal has been completed.

Methods: A consecutive series of the first 110 hip joints in 103 patients were followed clinically and radiographically for an average of 28 months.

Results: The mean Harris hip score rose from 43.6 points preoperatively to 91 points postoperatively. The mean pain score changed from 7.9 points to 42 points, respectively.

13 hips (11.8%) had mid-thigh pain, most of them mild. One hip (0.9%) showed clinical and radiographic signs of early loosening and was revised.

Conclusion: The short-term clinical and radiographic outcomes are encouraging. The double-threaded cone-shaped stem locking mechanism has been shown to be able to withstand the torsional and vertical forces applied to hip replacement prosthesis.