INTRODUCTION

Unicompartmental knee arthroplasty (UKA) has been shown to have many benefits over conventional Total Knee Arthroplasty (TKA), but has also been shown to be technically difficult. In fact, technical error is the most common cause of premature failure in UKA. Bicompartmental arthroplasty (BKA) has the potential to perform like TKA with the benefits of UKA. We describe the initial experience with customized alignment guides and implants for UKA and BKA, manufactured based upon preoperative CT scan.

INTRODUCTION

we have previously reported that bone preparation is quite precise and accurate relative to a preoperative plan when using a robotic arm assisted technique for UKA. However, in that same study, we found a large variation between intended and final tibial implant position, presumably occuring during cement curing. In this study, we reviewed a subsequent cohort of patients in which the tibial and femoral components were cemented individually with ongoing evaluation of tibial component position during cement curing.

Differences in femoral anatomy have been partially ascribed to gender differences. Traditionally, femoral stems for THA have been designed across an entire population including both males and females. The purpose of this study was to compare the applicability of two femoral stem systems in male and female populations via preoperative templating.

Methods: All patients seen during a single month who presented complaining of knee pain had screening pelvis x-rays. These x-rays formed a consecutive cohort of hips for the templating study. During templating, the acetabular component was placed in a fully medialised position at 45o of abduction. The center of rotation was marked. The femoral neck osteotomy was set at 15 mm proximal to the lesser trochanter. Templates of equal magnification were utilized for both systems. System 1 had a double tapered wedge body design, a fixed 135o neck-shaft angle with two different offsets (6 mm difference) and two different neck lengths (4 mm difference). There were 7 head options with different lengths. System 2 had the same body design with a modular neck offering 20 different offsets/lengths and 7 different neck-shaft angles, with only one head option. Neck length and offset were independent of body size for both systems. Based upon templating, the categories were: No obvious advantage of either system, System 1 preferred, System 2 preferred, Neither system appropriate. Preference was determined based upon providing at least one additional length or offset option, and avoiding the extra extended offset option in System 2 based upon the theoretical risk of disassociation due to extremely high moments.

Results: There were 20 female patients contributing 40 hips and 27 males contributing 54 hips. Among the males, there was no obvious advantage in 20/54 hips (37%), System 1 was preferred in 11/54 hips (20.4%), System 2 was preferred in 15/54 hips (27.8%), and neither system was appropriate in 8/54 hips (14.8%). In addition, System 1 could have been used in 33/54 hips (61.1%), while System 2 could have been used in 42/54 hips (77.8%). Overall, 46/54 male hips (85.2 %) could be implanted with this stem. Among the females, there was no obvious advantage in 17/40 hips (42.5%), System 1 was preferred in 1/40 hip (2.5%), System 2 was preferred in 13/40 hips (32.5%), and neither system was appropriate in 9/40 hips (22.5%). In addition, System 1 could have been used in 22/40 hips (55%), while System 2 could have been used in 31/40 hips (77.5%). Overall, 31/40 female hips (77.5 %) could be implanted with this stem.

Discussion: Significantly, there are gender differences in applicability of femoral stems. Specifically, more neck length and offset options seem to be required for females. One criticism of this study would be that the neck osteotomy length was fixed. In practical application, surgeons frequently adjust the level of the neck osteotomy to successfully reconstruct the hip. Further study is necessary to determine the role of neck-shaft angle, bone quality and adjustment of neck osteotomy height.

Restoration of proper alignment is one of the principle goals of TKA. Various methods are popular, including intramedullary (IM) and extramedullary (EM) mechanical guides, and recently computer assisted navigation (CAS). In addition, minimally invasive surgery has added an extra level of complexity to achieving satisfactory alignment. The purpose of this study was to determine the effect of approach (standard arthrotomy vs MIS) and alignment technique (Mechanical vs CAS) upon component alignment in TKA.

Methods. Three consecutive cohorts of patients were included: Group I--Standard arthrotomy with Mechanical guides; Group II-MIS approach with Mechanical guides; Group III-MIS approach with CAS. A single surgeon performed the Standard Mechanical cohort, and a second surgeon performed all surgeries in the other two cohorts. For the mechanical groups, IM femoral and EM tibial guides were used. For CAS, the Orthosoft system was used. All components were NexGen (Zimmer) Postoperative x-rays were used to measure component alignment relative to the IM axes, including femoral valgus and flexion, and tibial varus and slope, and patellar tilt. In addition, joint line position was measured. Students’ t-test was used to determine level of significance.

Results. For Groups I, II and III, there were 41, 38 and 39 patients, respectively. For femoral alignment in the coronal plane, results were 4.83+4.29 degrees, 3.82+2.72 degrees, and 3.36+2.49 degrees, respectively. Femoral flexion was 2.93+2.82 degrees, 3.18+2.93 degrees, and 2.46+2.79 degrees, respectively. Tibial alignment was 0.44+3.98 degrees of varus, 1.00+2.83 degrees of valgus, and 0.95+2.58 degrees of varus, respectively. Slope was 6.78+3.23 degrees, 3.23+3.21 degrees, and 3.93+2.85 degrees, respectively. Patellar tilt was 2.15+3.51 degrees lateral, 1.73+2.67 degres lateral, and 1.03+2.28 degrees lateral, respectively. The joint line was raised 1.18+3.54 mm and 0.05+4.92 mm in Groups I and III, respectively, and lowered 0.33+4.78 mm in Group II. There were no statistically significant differences in any measurement between any groups.

Discussion. Satisfactory alignment can be achieved with either mechanical guides or navigation systems. MIS approaches do not worsen alignment with either alignment methodology. Whether having fewer outliers translates into improved clinical outcomes remains to be seen. More importantly, CAS provides an intraoperative tool that may allow more accurate reproduction of a customized plan for an individual, rather than simply attempting to achieve the “mean” for a population. Again, the value of achieving such a goal is unknown since the threshold for improvement with off-the-shelf knee components may have already been maximised.

Unicompartmental arthroplasty of the knee (UKA) is technically challenging because the prosthetic devices must function in concert with a mostly normal joint. Malalignment is common, leading to patient dissatisfaction and early failures. However, UKA remains attractive as a temporizing treatment in early disease. Until now, resurfacing UKAs were performed with free-hand techniques. This study is only the second report investigating the use of a tactile guidance system (TGS—essentially, a robotically assisted surgery) for the performance of UKA.

Methods. The first 20 patients who underwent resurfacing using a Mako Surgical Inc. TGS system by a single surgeon were studied. Surgical goals were to place the components to replicate closely the patient’s native bony architecture. The surgical plan was completed on a workstation, and then executed with the TGS system through a mini-arthrotomy. Stelkast, Inc resurfacing components were implanted with methymethacrylate. Intraoperative measurements of component position were obtained. Pre- and postoperative radiographs were also measured for alignment correction, change in angulation of the joint line relative to the femoral and tibial anatomic axes, femoral component alignment relative to the femoral anatomic axis, and change in tibial slope.

Results. All cases could be completed as planned. None were converted to a full arthrotomy. None required conversion to a different implant. There were no failures of the TGS, associated navigation, or the CAT-scan based preoperative plan.

Intraoperative measurements showed an average femoral component position of 0.89+3.36 degrees of varus relative to the mechanical axis, with 62.5% being varus and 37.5% being valgus. The average femoral component flexion was 11.1+2.11 degrees, with no outliers (less than 5 degrees; greater than 15 degrees). The tibial component position was 4.60+1.76 degrees of varus, with all components in varus as desired. There was an average of 5.00+2.37 degrees of slope, with 25% outliers (less than 3 or greater than 7 degrees).

Postoperative measurements showed an overall limb alignment correction of 4.29+2.60 degrees, femoral joint line change of only 0.43+0.49 degrees, and an overall component alignment relative to the anatomic axis of 4.54+3.77 degrees of valgus. On the tibial side, the joint line varus was corrected by 3.00+2.04 degrees and the slope was changed by 4.29+3.24 degrees, including 19% outliers (less than 3 degrees, more than 7 degrees). However, 33% of the outliers were outliers preoperatively as well. Interestingly, the bone level after resection on the tibial side averaged 5.36+3.00 degrees of varus, suggesting that component placement must be carefully watched.

Discussion. TGS seems to be extremely accurate and precise in recreating individual patient anatomy. This also applies to cases in which the patient anatomy dictates placement of components in so-called “outlier” positions. It is unknown whether these “outlier” positions really translate into poorer outcomes. Impressively, there were no failures to execute the intended surgical plan and no failures of the TGS system. Future research will attempt to correlate component placement in native anatomical positions with functional outcomes and failures, as well as cost-effectiveness of the system.

Purpose of the Study: To assess the use of synthetic hydroxyapatite for postero-lateral spinal fusion using a new classification system

Methods: This is a prospective study on 30 patients who underwent bilateral postero-lateral spinal fusion between October 2002 and January 2004. The sides were randomised to synthetic phase pure Hydroxyapatite (Apapore® 70) mixed with bone marrow and autologus bone on one side and Apapore® 70 with bone marrow on the other. Plain Antero-posterior and Lateral x-rays were done in the immediate post-operative period and at 3, 6, 12 and 24 months. Two independent observers assessed the Antero-posterior films using a new classification system. Spine was considered fused when either or both sides showed good evidence of bone formation between the graft particles and graft and transverse process.

Results: In 6 patients x-rays were lost and 2 did not have two year follow-up. Twenty of the remaining 22 patients (90.9%) showed evidence of fusion as documented by both the observers. Good evidence of bone formation was noted as early as 6 months on the side where Apapore was used with bone marrow with 90.9 % achieving fusion at 2 years as against 57.1 % on the opposite side. The inter-observer agreement was good (mean 81.6%) with kappa score of 0.736.

Conclusion: The Hydroxyapatite based bone graft substitutes behave differently than autologus bone graft and poses difficulty in assessing fusion according to the radiographic classification systems described. The classification described above is useful in such situations and has shown to have good inter-observer reliability. With the increasing use of bone substitutes this classification system may be valuable in assessment of fusion and inter-study correlation.

Introduction: Proximal porous coating for cementless fixation of femoral stems enjoys increasing popularity. We report on the intermediate to long-term results with a circumferentially proximally coated stem with a non-porous cylindrical diaphyseal portion. The smooth stem provides temporary rotational stability so that proximal bony ingrowth can occur.

Materials and methods: Between 1991 and 1994, 124 Multilock stems were implanted in 101 patients. Patients were followed prospectively and re-evaluated at a minimum five years postop (range 60 to 117 months) by an author other than the surgeon. Four patients (5 hips) were lost to follow-up. Five patients (6 hips) had died. Twenty-six patients (30 hips) had phone interviews more than five years after surgery, but no radiographs as they refused to return for followup. None of these patients had required additional surgery and all were extremely satisfied with their outcomes. Sixty-six patients (83 hips) had clinical and radiographic followup at minimum five-years post-op. This report focuses upon this last group.

Results. The average age at surgery was 53.8 years (range, 27–75). The average follow-up was 78 months (range, 60–117). The average Harris Hip Score was 93 (range, 52–100). One stem had been revised for loosening (1%), and none were radiographically loose. Eight patients (9.6%) had minimal thigh pain related to excessive activity. These patients required mild analgesics only. Eighty-two stems (99%) achieved bony ingrowth. Twenty-nine stems (35%) had minimal osteolysis limited to Zones 1 and 7. There were no cases of diaphyseal lysis. Radiolucent lines adjacent to the porous coating were evident in 3 stems (3.6%), and along smooth portions in 20 stems (24%). No radiolucent lines were progressive or divergent. Some degree of stress shielding in the proximal metaphysis was evident in 52 hips (63%), but only 2 had cortical resorption.

Discussion and conclusion. Given the young age and high activity level of this cohort of patients, the Multilock stem has fared extremely well. Loosening and revision rates were very low, and distal osteolysis had not occurred. Bony fixation occurred reliably. Proximal stress shielding remains concerning and further follow-up will determine whether this becomes clinically significant. Lastly, patient function and satisfaction were high. In conclusion, the Multilock proximally porous-coated stem can be expected to perform well in the intermediate to long-term in young, active patients.

Introduction: A 2-stage approach is often employed to treat infected TJA. Success rates have been reported between 85–100%. Other authors favor multiple routine debridements (I& D) to lower the infection rate. This study compares the relative effectiveness of 2-, 3- and 4 stage treatment approaches.

Methods: Between 1988 and 1998, all infected TJA at our institution were treated with a 2-, 3- or 4 stage approach. In the 2-stage approach, prosthesis removal was followed by 6 weeks of IV antibiotics and reimplantation. In the 3-stage approach, an additional I& D was added 5–7 days after prosthesis removal. In the 4-stage protocol, a third I& D was performed after completion of antibiotics. Negative cultures led to reimplantation. Positive cultures led to an additional 6-week course of antibiotics, and then repeat 3rd and 4th stages. Patients retained their components if free of infection, on chronic antibiotic suppression or after additional I& D. Patients were free of infection if no more treatment was needed.

Results: 83 patients with infected TJA were treated. Average follow-up was 25 months. Of the 2 stage patients, 9/10 (90%) retained their components, and 7/10 (70%) was free of infection. Of the 3 stage patients, 32/37 (86%) retained their components, and 28/37 (76%) was free of infection. Of the 4 stage patients, 34/36 (94%) retained their prosthesis, and 30/36 (83%) was free of infection. Seventeen additional patients in the 4-stage group had positive cultures at the third stage. After additional treatment 13/17 (76%) retained their components and 12/17 (71%) was free of infection. No correlation was found between infection severity (gram positive vs. negative organisms; single vs multiple organisms) or initial diagnosis.

Discussion. Our ten-year experience with infected THA suggests that multiple I& D are required for successful treatment. Repeat I& D assures a sterile wound, as tissue culture is more sensitive than aspiration. Importantly, persistent infection after three I& D and appropriate antibiotics led to poorer results, suggesting that other host factors may preclude these patients from reimplantation. Given the exorbitant costs of treating failed reimplantations, an additional routine I& D may in fact be cost-effective across an entire population of infected TJA patients. Further analysis will focus upon cemented versus cementless implants, cost-benefit ratios of multiple debridements, nutritional parameters, functional assessments of patients at latest follow-up, cost analysis, and the value of preoperative.

Conclusion: We recommend a 4-stage approach to the treatment of infected THA.