Introduction: Failure to restore offset in severe protrusio defects in revision total hip replacement can lead to impingement and loss of limb length. The purpose of this study was to determine the initial results obtained with a novel cup in cup technique utilizing two porous tantalum acetabular shells, one placed onto supportive host bone in a cementless fashion, the other cemented in to this shell.

Methods: Porous tantalum hemispherical shells were implanted in 4 revision total hip replacements in 3 patients with an average age of 73 years at the time of the procedure.

Bony defects per the Paprosky classification were one IIC, two IIIA, and one IIIB. All patients were followed clinically and radiographically.

Results: The patients were followed for an average of 25.5 months (range, 17 to 29 months). Abductor strength improved by one grade in all patients. In the non-bilateral reconstruction patients horizontal offset was increased compared to the normal hip by 6 mm (IIIB) and 8 mm (IIC). For the bilateral reconstruction patient (IIIA) horizontal offset compared to pre-op was increased by 13–16 mm. There was no evidence of loosening or migration at the time of final follow-up.

Conclusions: At short term follow-up the early experience cautiously supports the use of this construct. Long term follow-up and a larger patient experience will be required to evaluate the results of this novel technique.

Previous in vivo studies pertaining to THA performance have focused on the analysis of gait. Unfortunately, higher demand activities have not yet been analyzed. Therefore, the objective of the present study was to determine the in vivo kinematics for THA patients, using fluoroscopy, while they performed four higher demand activities.

The 3D in vivo kinematics of 10 THA patients were analyzed during the following activities: pivoting (PI), tying a shoe (SHOE), sitting down (SDOWN) and standing up (SUP) with and without the aid of handrails. Patients were matched for age, height, weight, body mass index, diagnosis and femoral head diameter to control for confounding variables possibly having influence on the hip performance and kinematics of the various activities.

The largest amount, incidence and variation of separation (femoral head sliding in the acetabular cup) were achieved during the PI with 1.5mm (SD 1.1) and 9 of 10 (90%) subjects experiencing separation. For the SHOE, SDOWN and SUP activities the average separation values were 1.1, 1.2 and 0.7mm, respectively. Femoral head separation was observed in 8 of 10 subjects (80%) during SHOE, in 9 (90%) during SDOWN, and in only one of 6 (60%) during SUP.

In this present study, subjects demonstrated hip separation during the high demand subjects, which could be a concern because these same activities are subjected to higher bearing surface forces. Also, the presence of hip separation leads to reduced contact area between the femoral head and the acetabular cup, possibly leading to higher contact stresses.

Introduction and Aims: In the original randomised USFDA multi-centre clinical trial, the radiographic results showed superior surgical technique for ROBODOC, but at the expense of increased surgical time (258 min. vs. 134 min.) and blood loss (1189cc vs. 644cc). Although this did not result in any increase in complications, improvements in the method of registration (DigiMatch^TM) and faster cutting times have resulted in a more efficient procedure. This study represents a preliminary report of the blood loss and surgical time encountered in a new randomised controlled study of the DigiMatch^TM version of ROBODOC.

Method: This is an uneven randomised controlled study comparing primary THR using the DigiMatch^TM ROBODOC Surgical Assistant (Integrated Surgical Systems, Inc.) with the standard conventional technique. To date there are 80 consecutive patients (three bilateral) with 83 hips (65 Robodoc, 18 control). Inclusion and exclusion criteria, similar to those used in the initial USFDA multi-centre trial, were used in this study. The blood loss (as estimated by the anesthesiologist) and the surgical time (from incision to skin closure) were recorded and analysed using ANOVA.

Results: Average age (59.15 vs. 60.17 years) and weight (190.92 vs. 188.50 lbs.) were not significantly different (p> 0.65). The avgerage blood loss was also not significantly different (471.54cc for Robodoc vs. 405.56 for control, p=0.256) with a 95% confidence interval of −174.4 to +42.4cc. Surgical time was different at 121.92 min. for Robodoc and 85min. for control (p< 0.00). There was no difference in the need for transfusion. There were no device-related adverse events.

Conclusion: The results of this preliminary report of the DigiMatch^TM Robodoc Surgical Assistant, coupled with the prior finding of improved radiographic results, seem to validate the initial concept and indicate the potential clinical utility of the device. We anxiously await the combined results of the three centres currently participating in the study.

Introduction: Using Automated Implant Design and Analysis (AIDATM ) a library of femoral CT scans was analyzed. Design goals of fit and offset allowed generation of nine sizes each of right and left implants for off-the-shelf use. The five to nine year follow-up of 96 (12 bilateral) consecutive primary total hip arthroplasties using this titanium alloy hydroxylapatite (HA) one-third coated femoral stem is reported. The purpose of this study is to determine if the incorporated engineering design goals produced results equal to or superior to other published mid-term follow-up studies.

Methods: Seventy-five femoral CT scans from patients undergoing cementless primary total hip arthroplasty were used as the anatomic database. The stem was conceived as a metaphyseal filling implant with flat posterior and lateral sides. Prior micro-motion cadaver research of other stems by the authors has shown that stems with the best fit on the Medial and Anterior quadrants as well as the Medial-Anterior corner (“MAMA” fit) are the most stable. Therefore the medial and anterior surfaces were contoured and were given priority fit. Distally the stem was cylindrical, and allowed for diaphyseal contact over a distance of two outer canal diameters. Five modular femoral heads were assumed with the design goal to be within 5 mm of the existing head center in 95% of cases.

Results: The median Harris score is 91% (max 100) with 77% good or excellent. The mean pain score is 39.5 (max. 44) with 80% having none or slight pain. Ten hips (11%) have slight to mild thigh pain. One stem was revised for late loosening due to osteolysis. All others remain well-fixed (Engh grade I). Six hips were re-operated: two head & liner changes for recurrent dislocations and four for wear and acetabular osteolysis. Radiographic analysis showed all stems became well bonded over the HA coating with no RLZ’s and accretion of bone in the lower half of Zones 1 & 7 at the end of the HA coating. There was no subsidence. Stress shielding was limited to the upper half of Zones 1 & 7. Osteolysis was common above the HA coating around the shoulders of the implant, but extended distally in only one stem (revised).

Discussion & Conclusion: These results at Five-year minimum follow-up compare favorably with other published series of cementless stems at the same follow-up. The 100% incidence of ingrowth combined with the absence of stress-shielding below the upper half of Zones 1 & 7, serves to validate the design concepts and methodology used to create this implant.

Introduction: From June 1991 to June 1995, 256 consecutive total hip arthroplasties using the Duraloc 100 TM acetabular shell, manufactured by Depuy, were performed by two surgeons. The acetabular component featured a non-locking apex hole eliminator. In January 1995 the first patient with extrusion of the apex hole eliminator was seen. Since that time 21 patients, or 8% (21/256) have been seen with partial or complete extrusion. This study reports the outcomes and discusses a possible rationale for this finding.

Methods: The study group comprises 12 men, nine women, mean age was 59 years (32-86), mean weight 180 lbs. 18 (86%) femurs were cementless, three (14%) were cemented. Mean acetabular component size was 58 mm (52-64), with 18 acetabular liners manufactured with HylamerTM, and three liners EnduronTM. Sixteen (76%) liners were 10 degree hooded, and five (24%) were non-hooded. Eighteen (86%) femoral heads were ceramic, and three (14%) were chrome-cobalt. 15 (71%) femoral heads were 28 mm diameter, and six (29%) were 32 mm.

Results: Radiographs were obtained at routine follow-up in 20 (95%) patients. One (5%) patient had groin pain as the indication for radiographs. Four (19%) patients had complete extrusion in to the pelvis of the apex hole eliminator, and 17 (81%) had partial backout with the apex hole eliminator still within the confines of the acetabular component. On the antero-posterior radiograph visible pelvic osteolysis was seen in the four patients with complete extrusion of the apex hole eliminator, all in zone B. Zone one femoral osteolysis was seen in one patient with incomplete extrusion of the apex hole eliminator. Sixteen patients had incomplete extrusion of the apex hole eliminator associated with no visible radiographic pelvic or femoral osteolyisis. Two (10%) patients have undergone revision with curettage and allografting of the pelvic lesion and head and liner exchange. At the time of revision surgery liner motion was grossly obvious.

Discussion: The apex hole eliminator is neither watertight nor locking. Our hypothesis is that activity-related hydraulic pressure generated from excessive liner motion causes a high-pressure fluid leak into the pelvis. This fluid contains sub-micron particles generated by backside wear. The combination of particulates and fluid under pressure produces retro-acetabular osteolysis. The cyclic pressure then allows the non-locking plug to advance into the osteolytic pelvic defect.

Introduction: From September 1999 to September 2000, 75 consecutive primary cementless total hip arthroplasties (THA) were performed by two surgeons. All acetabular components implanted were the Interop ™ shell manufactured by Sulzer Intermedics. In September 2000, due to unexplained early aseptic loosening of several acetabular shells, use of this component was abandoned by the authors. In December 2000 Sulzer recalled certain lot numbers of the component. This study examines the to date performance of this group of patients.

Methods: Of the 75 patients, 42 patients were identified as being in the recall group and 33 were not. Patients were seen at routine post-operative follow-up and as indicated secondary to pain. All patients were examined clinically and radiographically. Hallmarks of early failure were moderate to severe weight bearing start-up pain and a circumferential lucent zone (without a sclerotic line) seen best on the Lowenstein lateral view.

Results: The timing of the failure was early (less than 6 months from implantation). In the recalled group eight patients have undergone revision and five are pending revision, resulting in a 33% (13/40) failure rate. Of those patients undergoing revision surgery, seven were found to have loose prostheses. One patient was revised due to unexplained pain and was found to have a well-fixed component. His pain has subsided. In the non-recalled group one patient had pain beginning at six months post-operatively, and radiographic signs of loosening. At revision the prosthesis was found to be loose.

Discussion: The purported cause of this early aseptic loosening is attributed to a mineral oil residue left after manufacturing of the component, causing inflammation and inhibiting bone ingrowth. The failure and subsequent revision rate is expected to rise. Our experience to date indicates that patients in the recalled group and symptomatic patients in the non-recalled group need to be closely followed. This high incidence of early failure of a cementless acetabular component has never before been reported.

Revision total hip arthroplasty, with retention of well fixed femoral and acetabular components and exchange of modular femoral heads and acetabular liners, is seeing increasing usage, primarily for the treatment of osteolysis or recurrent dislocations. The purpose of this study was to determine the dislocation rate after this procedure.

From January 1993 to December 2000, 54 patients underwent isolated head and liner exchange performed by two surgeons. These patients have been followed bi-annually with clinical and radiographic evaulation. There were 36 males and 18 females. Diagnoses at the time of revision surgery were recurrent dislocations in 27 and osteolysis in 27.

The overall dislocation rate was 11% (6/54). In the 49 non-constrained revisions, a 28 mm diameter femoral head was used in 27 and a 32 mm head in 22. At the time of revision, 60% of the femoral heads were lengthened, 40% were increased in diameter, and 25% were increased in both dimensions. Hooded or later-alised liners were used in 55% of the revisions. Operative stability was documented in all operative notes, and in 85% Ranawat’s sign was used to determine liner placement based on relative component version. The dislocation rate in the non-constrained revisions was 8% (4/49). Two out of five constrained revisions, performed for recurrent dislocations, subsequently dislocated. In this study isolated head and liner revision had a comparable dislocation rate to full revision total hip arthroplasty.

A common finding in acetabular revisions is loss of medial bone stock. Using a standard cementless hemispherical component, alternatives for reconstruction include medialisation of the cup, medial particulate allograft with rim fixation on host bone, or use of a “mega-cup”. A cementless shell that has 6 mm of lateral augmentation is useful in restoring the joint centre while at the same time achieving implant stability and increasing host bone contact without loss of additional bone.

From 1991 to 2000, a total of 142 acetabular revisions were performed with the Arthropor TM DP+6 implant (Joint Medical Products/J& J/DePuy). These patients have been prospectively followed bi-annually with Harris Hip Scores and monitoring of complications and radiographic findings. Average follow-up is 5 years (range 2 to 11 years).

Implant survivorship is 100%. There have been seven re-operations: one for infection (debrided), two for femoral revision and four head/liner changes for recurrent dislocations. Dislocation incidence is 7.8%. The average Total Harris Score at 5 years is 74.3, with an average Harris Pain Score of 34.9 (out of a maximum of 44). Radiographic analysis showed frequent zone 3 radiolucent zones. Initial migration of > 2 mm with subsequent stabilisation occurred in 18%. The joint centre was restored to within 5 mm of the contralateral hip in 85% of cases.

We have found this type of implant to be efficacious in the more common acetabular revisions where the loss of bone stock is mainly medial/cavitary, with an intact posterior column and small medial segmental defects.