Background

The use of robotics in joint arthroplasty was initiated in 1992 with the introduction of the ROBODOC® Surgical Assistant device for planning and active robotic preparation of the femoral canal in THA. From 1993–1996, an FDA trial was undertaken using pin-based fiduciary markers to register the CT to the robot coordinate system. From 2000–2006, a second FDA trial was initiated using a point-to-surface matching “pinless” registration system. Combined, these two studies offer the first long-term follow-up of robot-assisted THA using an active robotic system for preparation of the femoral canal during THA.

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.

Hap Paul was a unique individual. It is appropriate that this award should go a unique paper presented at this year’s ISTA. The name “Hap” comes from his initials Howard A. Paul. He was an outstanding veterinarian, but he was also much more than that. He had an insatiable curiosity combined with a quick mind and a surgeon’s practicality. His first love was research. After graduating from high school in Connecticut, he went to Notre Dame as a swimmer. He graduated with a degree in Microbiology and a strong desire to “cure cancer”. Acting on his dreams, as he always did, he decided to go to Paris to work with one of the pioneers of Interferon research. Never mind that he didn’t have a job and did not know a word of French. Of course he got the job and learned French playing rugby (hence his awful accent and colorful vocabulary). The funding ran out for the Interferon research, but he somehow got a shot at a spot in the veterinary school in Paris. He got married and finished his veterinary training. The veterinary thing worked out, but the marriage didn’t. He returned to the US after 9 years living in France, to attend the UC Davis School of Veterinary Science as a surgical resident in the small animal area. He met his wife, Dr. Wendy Shelton there… but that is another story.

I met Hap when I was a new attending orthopaedic surgeon at UC Davis and looking to do some animal modeling of hip replacement revision techniques. He was an imposing figure: six feet four, big curly afro and wire glasses. He dressed like a Frenchman, wore big clogs and carried a purse. Needless to say I was intimidated initially. But, he had great joi de vive and lived up to his name… he was almost always happy.

Hip replacement in dogs began in the 1970’s, but was nearly abandoned by the early 1980’s because of infections and “luxations” (dislocations). In order to develop an animal model we had to develop instruments and techniques that incorporated “third generation” cementing techniques. This we did, but Hap took these instruments and began using them clinically on working dogs. He developed quite a reputation for resurrecting hip replacements for dogs in the US and internationally. Hap and I went on to develop dog models for CT-based custom implants and later surgical robotics (eventually leading to the development of Robodoc). Despite our academic interests, both Hap and I went into private practice in the mid 1980’s… separately, of course (he as a veterinary orthpaedic surgeon and I specialized in hip and knee replacements for humans). Our research in surgical robotics took off when we landed a huge grant from IBM. But then the sky fell in when we learned that Hap had developed lymphoma. After surgery, radiation and chemotherapy, he was in remission, but temporarily couldn’t perform surgery due to a peripheral neuropathy attributed to Vincristine. So Hap went to the lab at UC Davis to work directly with the robotics team. He was a slave driver… but a pleasant one. Certainly the basic research behind Robodoc could not have been done without Hap getting lymphoma.

Over 5 years (1986–91) we both had a ball working with some of the best minds in robotics and imaging research. We presented our research on CT-based customs and robotics at many international venues, and Hap made many friends… some are in the audience today. He was one of the founders of this organization (ISTA). Hap returned to veterinary practice when he could finally work with his hands again… but this was not for long. Soon our research lead to the founding of Integrated Surgical Services (ISS) in 1991, the makers of Robodoc. Hap agreed to leave his practice to lead the company and I stayed in clinical practice to develop and utilize the device on patients. In 1992, we shocked the world by being the first to use an active robot in human surgery. It looked like the dawning of a new age. (I still believe it is, but it has been a very slow dawn).

For Hap, the joy was short-lived. He developed leukemia as a complication of his prior chemotherapy. He died while recovering from a bone marrow transplant on Feb. 10, 1993 at the young age of 44. During his short life he contributed tremendously to the benefit of others by his research and development work. But mostly he inspired others to excel in their endeavors. He was a wonderful guy. And we are all pleased to honor him with the presentation of the Hap Paul Award at each year’s meeting of ISTA.

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 and Aims: Genetic defects causing dwarfism occur in approximately one in 10,000 live births. There are over 200 types, with achondoplasia, spondyloepiphyseal dysplasia, diastrophic dwarfism and hypopituitarism being the most common. Another frequent cause of short stature is juvenile rheumatoid arthritis. Most types of dwarfism result in arthrosis of major joints, resulting in significant disability. Hip replacement can offer significant improvement in quality of life, but there are inherent difficulties due to size and anatomic variations.

Method: Short stature of less than 4 feet 10 inches was defined as dwarfism. Eight patients meeting this criterion underwent total hip replacement, either primary or revision, with six being bilateral, resulting in a total of 14 hips for study. The diagnoses were: two JRA, two Mucolipdosis III, one Dyastrophic Dwarfism, one Spondyloepiphyseal Dysplasia, one Thalasemia, and one Congenital Rickets. In each case, a CT-based custom cementless femoral component was used. The patients were followed prospectively with the Harris hip scale and serial radiographs. Average follow-up was nine years (two to 14).

Results: The average total Harris hip score improved from 35 pre-operatively to 66 at last follow-up, with the average Harris pain score increasing from 10 to 31 (out of a maximum of 44). Five hips have been reoperated: two for combined acetabular and femoral loosening, one for acetabular loosening, one for recurrent dislocation and one for late hematogenous infection.

Conclusions: Hip replacement in dwarfs presents a complex technical challenge, but can result in significant improvement in pain, function and quality of life. CT-based custom femoral components are recommended.

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: Patient specific cementless femoral components for THR were developed as a means of addressing the anatomic variations of the proximal femur and hip joint in an effort to achieve long term implant survival and optimum patient function. Design rules were developed with goals of achieving rigid initial stability, maximal endosteal contact for bone integration, and the precise restoration of hip kinematics.

Methods: Beginning in 1989, this series of cementless titanium implants included proximal circumferential HA coating over a macrotextured surface for biologic fixation. All patients who were candidates for cementless arthroplasty (age < 65, active, or overweight) received a custom femoral component. Forty-nine consecutive primary THR in 39 patients were performed during the study period. No patients died and one patient was lost prior to 10 years; all had well fixed stems at latest follow up. The remaining 38 patients (48 hips), 16 females and 22 males, with average age 54 (28-70) and weight 181 (98-270) at surgery, were evaluated at minimum 10 years (range 10-11).

Results: Average modified Harris Hip Scores were 49 (27-87) pre- and 89 (24-100) postoperatively, with pain scores of 17 (0-40) and 42 (10-44) respectively. All femoral components remain well-fixed (Engh Class 1) at final follow-up. No areas of osteolysis were seen distal to the proximal HA-bone interface. Small, focal areas of probable osteolysis were seen at the implant shoulder (4 cases), at the calcar corner (2 cases), and at both sites (1 case). Complications included four proximal margin femoral fissures recognised at surgery, two patients with dislocation, and one non-fatal PE. Reoperations included six head and liner exchanges; two for recurrent dislocation, and four for excessive wear with associated osteolysis (3 pelvic, 1 femoral); and one for fixation and grafting of a trochanteric nonunion.

Discussion: The use of cementless femoral implants based on individual patient characteristics and a set of strict design rules has resulted in excellent clinical and radiographic results at 10-year follow-up. Recent data with some OTS systems have shown comparable excellent results and have diminished the need for the routine use of custom implants in uncomplicated primary situations. However, this series validates the design concepts of this system, supports its use in more complex situations, and suggests applicability on a routine basis where other available implants may be less than optimal.

Introduction: Conventional approaches to cementless revision THR include cemented and cementless stems, which are graft dependent for initial stability (Type 3 reconstructions), distally fixed extensively porous coated implants and modular implants. CT and radiographic visualization, preoperative planning, and patient specific implant fabrication enable the surgeon to achieve the following objectives simultaneously and without compromise: bypass or fill specific bony defects, implement precisely the surgeon’s individual implant design goals, optimise proximal, distal, or regional fit objectives, achieve supplemental fixation via collars, fluted stems, and targeted ingrowth zones/ treatments, and establish head center, neck length, lateral offset, anteversion angle, and leg length.

Methods: This series of cementless titanium implants achieved initial press-fit fixation on host bone with bony attachment via proximally HA coated macrotextured surface. The extramedullary portion of the implant is designed to restore leg length and normal joint mechanics. The initial 44 consecutive revision hips using this rationale were reviewed for inclusion. At surgery, all femoral reconstructions were completed without resorting to Type 3 structural grafts. Six patients died prior to 10 years f/u, and three (4 hips) were lost. Two stems were removed prior to minimum follow up: one at five weeks post-op for deep sepsis, and one for aseptic loosening presumed secondary to metabolic derangements from poorly controlled end-stage renal disease. The remaining 31 patients (34 hips), 18 females and 13 males with a mean age of 61 (range 31-75) and average weight of 168 (85-240) pounds, were evaluated at minimum 10 years (range 10 to 11 years).

Results: All 34 components remain well-fixed (Engh Class 1) at last follow up (97% implant survival). Stress shielding was uncommon outside the calcar region. Average modified Harris Hip Scores were 49 (10-88) pre-operative and 81 (48-100) at final follow-up, with pain scores of 18 (0-44) and 41 (30-44) respectively. Complications included fracture (intraop: 4 fissures, 2 stable type II, 1 unstable type III, and 1 late periprosthetic fractures distally), and three dislocations.

Discussion: The concept of a metaphysical loading, proximally ingrown, collared patient specific revision implant gave results comparable to Engh’s series of extensively coated revision stems, while avoiding the high failure rate associated with structural allograft, the worrisome proximal bone loss associated with fully porous coated stems, the high cost of modular implants.

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.

Genetic defects causing dwarfism occur in approximately 1 in 10 000 live births. There are over 200 types. Another frequent cause of short stature is juvenile rheumatoid arthritis. Most types of dwarfism result in arthrosis of major joints resulting in significant disability. Hip replacement can offer significant improvement in quality of life, but there are inherent difficulties due to size and anatomic variations.

Short stature of less than 4 feet 10 inches was defined as dwarfism. Eight patients meeting this criterion underwent either primary or revision total hip replacement, with six being bilateral, resulting in a total of 14 hips for study (six primaries and eight revisions). The diagnoses were: two JRA, two Mucolipdosis III, one Dyastrophic Dwarfism, one Spondyloepiphyseal Dysplasia, one Thalasemia, and one Congenital Rickets. In eight hips a CT-based custom cementless femoral component was used. Average follow-up was nine years (2 – 14).

The average Total Harris Hip Score improved from 35 pre-operatively to 66 at last follow-up, with the average Harris Pain Score increasing from 10 to 31 (out of a maximum of 44). Of the six primary hips, two hips in the same patient have been revised for combined acetabular and femoral loosening. Of the eight revision hips, there have been three re-operations: one re-revised for acetabular loosening, one re-revised for late hematogenous infection and one head/liner change for recurrent dislocations.

Hip replacement in dwarfs presents a complex technical challenge, but can result in significant improvement in pain, function and quality of life. CT-base custom femoral components are recommended.

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.