Introduction

Sagittal pelvic tilt (SPT) can change with spinal pathologies and fusion. Change in the SPT can result in impingement and hip instability. Our aim was to determine the magnitude of the SPT change for hip instability to test the hypothesis that the magnitude of SPT change for hip instability is less than 10° and it is not similar for different hip motions.

The position of this surgeon is that there is no approach that provides superior outcomes for total hip replacement (THR). The direct anterior approach (DAA) has become popular with patients because of marketing by companies, misinformation given to journalists for public consumption, and yes, some surgeons. Because of patient pressure generated by this marketing there has been pressure on surgeons to convert their surgical approach for perceived protection of their practice. Unfortunately, the leaders of orthopaedic organizations have not countered this marketing with education of the public that there is NO scientific evidence to support DAA superiority. These orthopaedic organizations exist to be advocates for their members but have abdicated that responsibility. Whatever happened to the time honored belief of choosing a surgeon to do your operation? Instead we now choose an approach? Do anterior surgeons think that they are immune to the Bell Curve of talent? The fact is that there is NO outcome data of DAA with the longest follow up study being one year, and recent data from both coasts of the USA raise concerns with more failures from loosening of the femoral component. How in the world can we bamboozle patients about better results when there are no published results with the DAA except for recovery? The mini-posterior approach has data for all aspects of its use. Short term data shows rapid recovery and hospital discharge can be the same day; gait studies show A quality at six weeks (so does this mean that cut muscles recover quickly?). Dislocation rates are equal in most comparative studies, but I believe this favors the DAA, however, fractures are 3X greater with DAA. Data from the Mayo Clinic comparative studies showed posterior patients return to work faster! There are two 10 year studies of mini-posterior patients which show some of the best 10 year results in the literature. And there are superior technical surgeons who perform this operation to the benefit of their patients, and they should not need to suffer the implicit bias from DAA marketing that their care of patients is inferior.

Dorr bone type is both a qualitative and quantitative classification. Qualitatively on x-rays the cortical thickness determines the ABC type. The cortical thickness is best judged on a lateral x-ray and the focus is on the posterior cortex. In Type A bone it is a thick convex structure (posterior fin of bone) that can force the tip of the tapered implant anteriorly – which then displaces the femoral head posteriorly into relative retroversion. Fractures in DAA hips have had increased fractures in Type A bone because of the metaphyseal-diaphyseal mismatch (metaphysis is bigger than diaphysis in relation to stem size). Quantitatively, Type B bone has osteoclastic erosion of the posterior fin which proceeds from proximal to distal and is characterised by flattening of the fin, and erosive cysts in it from osteoclasts. A tapered stem works well in this bone type, and the bone cells respond positively. Type C bone has loss of the entire posterior fin (stove pipe bone), and the osteoblast function at a low level with dominance of osteoclasts. Type C is also progressive and is worse when both the lateral and AP views show a stove pipe shape. If just the lateral x-ray has thin cortices, and the AP has a tapered thickness of the cortex a non-cemented stem will work, but there is a higher risk for fracture because of weak bone. At surgery Type C bone has “mushy” cancellous bone compared to the hard structure of type A. Tapered stems have high risk for loosening because the diaphysis is bigger than the metaphysis (opposite of Type A). Fully coated rod type stems fix well, but have a high incidence of stress shielding. Cemented fixation is done by surgeons for Type C bone to avoid fracture, and insure a comfortable hip. The large size stem often required to fit Type C bone causes an adverse-stem-bone ratio which can cause chronic thigh pain. I cement patients over age 70 with Type C bone which is most common in women over that age.

Short stems are an option for primary THR, but these are the technical challenges. Stem anteversion is increased with short stems usually above 20 degrees so cup anteversion must be adjusted lower. Offset is better if increased up to 5 mm more because more bony neck is retained and with increased stem anteversion the greater trochanter is more posterior, and both of these increase the risk of bony impingement. Short stems are best in A bone, okay in B bone, not recommended yet in C bone. With standard stems performing so well use caution for conversion to short stems.

Dislocation and accelerated wear have been the nemesis of hip surgeons. No study has been able to correlate cup position to instability. In recent years the influence of the spine-pelvis-hip construct has emerged as important to understand the shift in component position with postural change.

Using measurements familiar to spine surgeons, we have correlated the pelvic incidence (PI), a static measurement of pelvic width and hip position; the static tilt, a dynamic measure of pelvic-spine mobility. For THR we have measured the sagittal cup position as the fixed angular change of the cup shifts with pelvic tilt, and this is named anteinclination; and the sacral acetabular angle (SAA) which is the relationship of the acetabulum to the absolute value of sacral tilt (ST) in both standing and sitting. The pelvic femoral angle (PFA) is a measure of femur/hip flexion/internal rotation correlated to pelvic mobility.

Dislocation is most common in patients with low PI combined with an ST change <15 degrees. With normal PI and high PI, it occurs much less commonly and only in patients with ST change <5 degrees (very stiff). In patients with stiff pelvis (ST<13) the cup needs increased inclination and anteversion (45/20–25) to compensate for absence of cup opening by posterior tilt of pelvis. For patients with low PI and stiff pelvis we recommend constraint (such as dual mobility articulation).

A well designed constrained liner does not have a “hood” nor a wide poly brim that extends beyond the metal shell because these cause impingement. The failure of a good design is almost always technique.

Size the liner so the poly is press fit against the metal rim of the cup. Cement thickness does not matter. Remove any derotation tabs on metal rim with a carbide burr so there is a firm press fit with no toggle. Do NOT angle the poly to change the anteversion.

Use the carbide burr to scratch the inner surface of the cup and a soft tissue burr to scratch the backside of the poly.

Cement must be liquid enough to fully seat the poly against the metal rim. If cement too doughy it resists full seating.

Put metal ring in groove during implantation and cementing to prevent cement into the groove.

If this is a primary cup use screws with the cup or cement the poly into the acetabular bone.

Dry the head and inner surface of the poly to facilitated reduction. Align the head concentrically into the mouth of the poly and push simultaneously on the knee and over the greater trochanter.

Revision of M-O-M articulation:

Indications

Loose cup either radiographically or clinically. Clinical symptoms are persistent startup pain; straightening from the bent position; inability to do single limb stance; limp.

Unrelenting pain with any activity, even turning over in bed.

Soft tissue mass in groin or anterior hip (more common anterior to greater trochanter than posterior.

Elevated ion levels, especially cobalt. Elevated is 10µg/L but dangerous levels not defined (my definition is 40µg/L. Danger is cobalt poisoning. Also elevated ions almost always mean increased wear so local osteolysis and bone destruction is a risk with increased follow up.

Cobalt poisoning: objective findings are cardiopulmonary with increasing shortness if breath; second most common is cognitive change. (Memory loss, psychomotor retardation). Subjective finding is psychological effect of a poison in their body.

A cemented stem is certainly a good technique to choose for patients 75 years of age or older. In Europe, cemented stems remain prevalent for all ages. In my experience a patient with a cemented stem is comfortable sooner and the leg is also stronger sooner. Cement technique is the most important factor of a cemented stem and with good technique these stems have shown 30 years of longevity in published follow up studies.

Technical points: 1.) Broach only. No reaming. 2.) Maintain hard cancellous bone in the metaphysis. Do not keep weak, loose bone. Brush loose bone away. 3.) Irrigate the femur until the irrigant is clear. Pack it with absorbent gauze (we use Kerlix). 4.) Place a plug and insert cement with a gun and manually pressurise the cement until you feel strong back pressure. 5.) The stem should be press-fit into the cement to force interdigitation of cement into the bone. This means the cement cannot be liquid when the stem is inserted. It must be doughy. 6.) The cement mantle should be 2–3mm circumferentially so pick the correct stem size to permit that. A centraliser will help centralise the tip of the stem in the cement column and prevent the stem being against the edge of the bone which breaks the cement column.

When a constrained liner is used in a non-cemented cup it is advisable to add screw fixation to the cup even if the cup has an excellent press-fit because there is more pull-out pressure on the liner with a constrained cup. It also is necessary for the cup to be in the correct anteversion/inclination. It is not advisable to use a constrained liner to “make up” for poor cup position. The patient can still dislocate and then that will require an open reduction.

Our most common use with constrained sockets is to cement a liner into a well fixed cemented cup. We also will cement the liner into two-stage infections to keep it stable between those operations. Failure with the cemented liner into a non-cemented cup only occurs with poor surgical technique. There is only one correct surgical technique and violation of this can cause disassociation of the liner from the cup or dislocation of the head from the liner. The correct technique is: 1.) Preferably there is no hood on the liner because that can increase impingement. 2.) The liner size must have a press-fit of the liner edge to the edge of the metal shell. This is absolutely critical. The liner size cannot sink into the shell or be proud of the shell. 3.) The liner cannot be tilted in the shell to change anteversion or inclination. 4.) The backside of the polyethylene liner must be roughened with a high speed bur preferably in a spider web design. 5.) The inside of the cup should be roughened with a carbide bit of a high speed drill. The screw holes should be cleared of fibrous tissue. 6.) The cement thickness is not a critical factor and 1–2mm is always sufficient. 7.) Maintain pressure on the liner with one size smaller pusher (28mm for 32 inner diameter liner) until the cement is hard.

The acetabular component is the most troublesome implant. There is more written about acetabular placement than any other anatomical site. The problems are: Maintenance of center of rotation (COR); Coverage of the cup with correct inclination and anteversion; Maintenance of inclination below 50 degrees; Anteversion must be mated to the femur (combined anteversion).

COR is critical for balance of the correct offset and leg length. The inferior-medial metal edge of the cup should lie over the TAL or just proximal to it. No cortical bone of teardrop is palpable.

Coverage: Inclination of the normal bony acetabulum has a mean of 55 degrees (range to 70 degrees) so the posterior-superior edge of the cup may be uncovered in many hips to keep inclination below 50 degrees. 45 degrees is critical for wear and anteinclination. Anteversion of the cup is not independent of the femur (Brown/Callaghan, Hip Society Award paper). Femur anteversion must be known to precisely position the cup. Cup coverage is important here too. The posterior and anterior edges cannot be proud (may need to ream more medial).

Cementless fixation has become dominant for THR throughout the world, but are all stem geometries equivalent in results? Registries are the best source for studying this question because they are absent of personal bias. Results at 5 years allow separation of implants so this time frame was used. Comparing the same articulations (ceramic or metal-on- polyethylene), cementless stems with proximal enhancement (elliptical shape), or a tapered stem with rectangular cross section, have performed better than stems with a slim (blade) AP geometry. Almost all cementless stems reported to registries today are broached only tapered in design.

Introduction

Recent gains in knowledge reveal that the ideal acetabular cup position is in a narrower range than previously appreciated and that position is likely different based on femoral component anteversion. For that reason more accurate acetabular cup positioning techniques will be important for contemporary THA. It is well known that malalignment of the acetabular component in THA may result in dislocation, reduced range of motion or accelerated wear. Up to 8% of THA patients have cups malaligned in version by more than ±10° outside of the Lewinnek safe zone. This type of malalignment may result in dislocation of the femoral head and instability of the joint within the first year, requiring reoperation. Reported incidences of reoperation are 1-9% depending on surgical skills and technique. In addition, cup malalignment is becoming increasingly important as adoption of hard on hard bearings increases as the success of large head hard on hard bearings seems to be more sensitive to cup positioning. This study reports the accuracy of a haptic robotic system to ream the acetabulum and impact an acetabular cup compared to manual instrumentation.

Introduction: Navigation increases the precision and reproducibility of reconstruction in THR. It is important for the surgeon to be able to trust the reproducibility of the navigator and that navigated surgery should produce better results than those obtained by the surgeon by himself. The aim of this study is to determine the reproducibility and trustworthiness of a navigation system for acetabular reconstruction and to compare the precision of the navigator with that of the surgeon.

Materials and methods: A total of 101 THRs were carried out in 99 patients using image-free navigation. The precision and reproducibility of the navigator were measured with 30 postoperative CT scans. The blind estimates of the surgeons for inclination and anteversion were compared to the values of the navigator; the navigator was as accurate as the surgeon in 101 cases.

Results: The precision of the navigator for inclination was 4.4° with a reproducibility of 0.03 and for ante-version it was 4.1° with a reproducibility of 0.73. The precision of experienced surgeons for inclination was 11.5° and 12.3° for anteversion (less experienced surgeons had a precision for inclination of 13.1° and for anteversion of 13.9°).

Conclusions: Computer accuracy for the real value of a CT scan is always within 5°. The estimations of the surgeons with mechanical guides, experience and good judgment are about 12 degrees that of the navigation system. However the percentage of values 5° higher than the desired levels in experienced surgeons is seen in about 30% of cases (in less experienced surgeons, in about 50%). The computer can eliminate acetabular malposition to within about 5 degrees for desired values and in this way improve stability and wear.

Introduction: The long-term results of total hip replacement can be improved by accurate placement of the implants, leading to restoration of hip biomechanics and prevention impingement from of implant malposition. Pelvic obliquity from patient positioning during surgery prevents accurate intra-operative assessment of component placement. Computer navigation assisted total hip replacement can potentially eliminate these problems by providing feedback on prosthetic placement during surgery. The purpose of our study was to assess the accuracy of the component placement in computer navigation assisted THRs performed in our institution.

Methods: A total of 154 computer navigation assisted total hip arthroplasties performed between January 2004 and January 2005 were prospectively included in this study. Image free optical based navigation system (Navitrack™) was used. All procedures were performed by the senior author using MIS and open posterior approaches. Two independent observers performed analysis of the position of components and leg length discrepancy from standardized hip radiographs. Navigation values during surgery were compared with postoperative radiographic evaluation.

Results: The mean abduction and anteversion angles of acetabular component in postoperative radiographs were 41.4 ± 6.1 and 22.6 ± 3.8 degrees respectively, in comparison to the navigation values of 40.9 ± 4.0 and 22.9 ± 3.6 degrees respectively. The femoral neck offset and leg length discrepancy calculated from navigation were with in a mean of 1.5mm and 2.8mm, respectively. There was one complication consisting of a peri-prosthetic femoral fracture that was recognised during surgery and treated with revision of the femoral component to a long-stem prosthesis. There was no early post-operative dislocation or deep infection in this series.

Discussion: This study showed that computer navigation assisted THR provided predictable and reproducible results with accuracy in component placement and restorations of femoral neck offset and leg length.

Introduction: Technical and patient care improvements have occurred with the posterior mini-incision total hip replacement (THR). The hypothesis of this study was that these changes would provide better results for patients in the posterior mini incision surgery (MIS) THRs performed in our institution.

Methods: The clinical and radiographic results of 100 THRs performed with the posterior mini incision between January 2004 and October 2004 were compared with 100 mini incision THRs performed between December 2001 and September 2002. The second group was subjected to improved operative technique, the post-operative analgesia protocol, rehabilitation and patient advise. The acetabular cup abduction angle, anteversion angle, and stem varus/valgus alignment angle were measured in the post-operative radiographs in both groups. Pain score and Harris hip score were recorded at 6 weeks and 3 months. Statistical analysis was performed using Student 2-tailed t test, Chi-squared test and Wilcoxon-Mann-Whitney tests to compare the incision length, operative time, estimated blood loss, length of hospital stay, pain score and radiographic measurements between the two groups.

Results: The results showed that the component positions were not compromised in either group. There were statistical improvements in 2004 group with less estimated blood loss, decreased hospital stay, reduction of postoperative pain and opioid analgesic use and earlier muscle recovery. In 2004 group there were no complications of infection, dislocation, or sciatic palsy.

Discussion: The posterior mini-incision operation has shown improved results with experience and changes in technique and patient care treatment. We have continued our practice using this new technique.

Total knee replacement (TKR) has always been one decade behind total hip replacement (THR). Successful changes have been slower to develop and less creative. The response to failures of the 1980s was to reduce risks with TKR, while in hip surgery the response was to raise the bar one or two notches higher in risk-taking. Part of the risks taken by hip surgeons who promoted non-cemented fixation during the decades of the 1990s was certainly different than that by proponents of non-cemented knee surgery and the resultant confidence level in the fixation in these two different joints is evident. Furthermore, data on results with total knee replacement, both cemented and non-cemented, has been less available in the decade of the 1990s for TKR as opposed to THR. Part of the reason for decreased creativity and risk taking with TKR is that cemented fixation of the knee has performed remarkably well for tota1 knee replacement. Almost all of the long-term results of success with total knee replacement, including the Total Condylar and the Insall-Burstein knee, have been with knee replacements that were performed with cement including cemented patella replacement. The survivorship of these cemented implants at 15–20 years remains nearly 90%.

Several factors influenced both the increased number of failures with non-cemented implants and the loss of confidence among orthopaedic surgeons for the use of non-cemented fixation with TKR. Firstly, the PCA knee had a high number of failures because of the bad plastic inserts that were used for the tibia. The heat pressed polyethylene delaminated fairly rapidly and created a significant number of failures that were associated with severe osteolysis which created a good deal of fear for non-cemented fixation. In addition, all the non-cemented implants were using metal-backed patellae, which resulted in 20–25% revision rates for at least the patella in PCA, Miller-Galante, and Ortholoc prostheses. Finally, the initial design of non-cemented implants including the PCA and the original Ortholoc knee were too flat-on-flat and this contributed to the high amount of wear and failures from instability over time with these knees. Combination of complications confounded the evaluation of the fixation of these non-cemented implants and the risks needed to improve the fixation method were not taken.

Presently, cemented fixation still dominates as the fixation of preference for orthopaedic surgeons performing total knee replacement. The confidence level with cemented fixation is very high and the results continue to be outstanding with the use of cemented fixation. One of the reasons for this is that the average age of patients who have a total knee rep1acement is 68 and therefore most patients that are 70 years of age or older can easily achieve the durability with cemented fixation that is necessary for them to have only one operation during their lifetime. At the present time cemented fixation is recommended for patients older than 70 years and the use of an all-polyethylene tibia is just as effective as a metal tray in these patients. In fact, with the data from Engh on particle formation with metal trays, the use of an all-poly tibia may be preferable.

In the last two to three years of the 1990s there was a resurgence of investigation into total knee replacement without using cemented implants. One of the most prominent of these was the treatment of the patella. There were several studies, including those of Whiteside, Barrack, and others that showed that the use of no patella button at all did give satisfactory clinical results, which were difficult to differentiate from patients with patella replacement. Secondly, the LCS mobile bearing knee reported results at 15 years that showed that non-cemented fixation actually had some areas of superiority to cemented fixation. These results did demonstrate to the orthopaedic community that a knee design which had a good articulation surface that did not cause accelerated wear and osteolysis could perform as well as knees with cemented fixation. Results with the Natural Knee also demonstrated that except for failures by wear in those patients who had thin polyethylene, the fixation of the implants was universally excellent at 10 years postoperative. Finally. Leo Whiteside settled on a central fluted grit blasted stem for fixation of the tibia and achieved excellent and immediate fixation with his Profix implants. The recommendation by me at this time is that non-cemented fixation is preferable for patients under the age of 60.

In revision knees the most common technique has been the use of non-cemented stems with cemented metaphyseal fixation. However, the problem with this fixation method is that the metaphysis often is very weak bone or has an absent bone and this results in poor rotational support for the metaphyseal implant. The non-cemented stem of the knee is not as stable in the diaphysis of the femur as is the proximal femoral stem in a press-fit situation. Therefore, if rotational constraint is lost at the metaphysis, the entire femoral implant has a significantly increased risk of being loose. Therefore in older patients I believe that a cemented stem is much more preferable. Older is defined as patients over the age of 70. The press-fit stem in the tibia provides more fixation than it does in the femur so that tibial fixation has more expectation of durabi1ity. However, again I believe the surgeon can use cemented fixation of the stem and the tibia in patients over the age of 70 with an expectation that it will be as durable as the non-cemented stem.

In the future, there will be an increased used of mobile bearing knees because of the theoretical benefit that in more active patients the wear would be better. Since these knees will be initially directed towards more active patients, the use of non-cemented fixation would also be desirable. The LCS knee has demonstrated that with a mobile bearing design, non-cemented fixation is durable. The use of fixed bearing knees is being expanded to a younger population also. Younger patients are asking for total knee replacements because of the successful use of this operation during the 1990s. In these younger patients, non-cemented fixation should be just as beneficial as it is felt to be for total hip replacement. The Natural Knee has proven that the fixed bearing designs can indeed be durable with non-cemented fixation. Finally, the success with hip replacement and the yearly increasing numbers of hip replacements that are performed by non-cemented fixation demonstrate that the orthopaedic community is gaining more and more confidence with non-cemented fixation. The increased knowledge of bone and the increased knowledge of the causes of osteolysis are helping to provide more and more success with non-cemented fixation. For these reasons, I believe that in the future non-cemented fixation will become the standard for total knee replacement.

A polyethylene liner can be cemented into a well-fixed and well-oriented acetabular component with success. This technique has been used by us for over 5 years. In the last year, we have used this technique in patients that are considered to be unlimited community ambulators and who participate in vigorous exercises as well as sports such as golf and skiing. These cemented inserts have therefore functioned in patients who have activity levels, which vary from a household ambulator to an unlimited community ambulator.

We have reviewed 17 patients with 18 hips that have follow-up beyond 2 years. Ten of these patients had the cemented insert performed because of dislocation and a constrained liner was inserted into the shell. Seven of these patients had a liner cemented at the time of revision because either the locking mechanism of the cup was not good enough to replace the liner or a new bearing surface was desired by the patient. Twelve of the liners that were cemented into the shells were constrained and five were standard polyethylene articulation surfaces (without constraint). Two of these were crosslinked polyethylene liners. At the time of revision eight hips also had stem revision and in nine hips only the modular femoral head and insert were exchanged.

There have been three revisions of these 18 hips. In the second hip replacement performed, the size of polyethylene used was too large and the ledge of the polyethylene rim was not abutted against the metal rim of the shell (the poly stood proud). This polyethylene disassembled within three months and a revision of this cup was done to a constrained cup and liner. The second revision was in a patient who had a cup changed with a standard polyethylene liner for dislocation. The dislocation persisted so that this patient was reoperated five months later and a constrained liner was cemented into the acetabular shell, which successfully stopped the dislocation. The third was a patient who had a constrained liner cemented into a cup, but continued to dislocate even with the constrained liner. There was no loosening of the cemented constrained insert. This patient had the entire cup revised to a ring support with a new constrained liner. In all three of these patients there was profound gluteus medius muscle absence of function.

Radiographic review of these acetabular reconstructions show that in those patients who had screw holes in the acetabulum there are no radiolucent lines apparent around the cement “puffs” which are visible in the acetabular bone. In those cups that did not have screw holes, the inner aspect of the acetabular cup was roughened with a Midas-Rex and there is no visible cement outside these cups. All of the acetabular plastic liners had the backside roughened with the Midas-Rex prior to being cemented into the metal shell.

Lever-out strengths of cemented polys into metal shells have shown that this is stronger than that provided by a regular locking mechanism.