Introduction:

Current pelvic plane software is not accurate and do not address normal acetabular center axis that has minimum impingement and maximum stability relation with femur in navigated THA

Introduction:

Purpose of mini-invasive hip arthroplasty, is least damage to skin and muscles. Unlike Roettinger modification to Watson-Jones, our approach requires no special table or instruments. Besides, direction of skin incision is perpendicular to interval between glutei and tensor muscles, thus called a Crisscross Approach. Incision is at direction of retractors causing less skin damage; and parallel to femur allowing expansion. No tendon or muscles are severed achieving a true inter-muscular non invasive approach. Unlike anterior approach, femoral circumflex vessels and lateral femoral cutaneous nerve are spared.

Introduction

The prevalence of reversing of extension coronal deformity during flexion and how that may change the routine algorithm of soft tissue balancing in total knee arthroplasty (TKA) has not been published. We name this phenomenon, the reversing coronal deformity (RCD). We observed 12% (45 patients) of coronal deformities consistently reverse in flexion in the osteoarthritic knees before surgery. We conclude that RCD phenomena need to be addressed in every TKA and collateral ligament release need to be modified or avoided; otherwise postoperative flexion instability may be inevitable. Femoral rotation adjustment with posterior capsule release has to be attempted first in RCD patients.

As much as there is interest in mini-invasive surgery (MIS) total hip arthroplasty (THA), there is controversy ranging from a more advantageous to a potentially dangerous alternative to classic THA. The purpose of this study is to compare the results of 130 cementless, standard stem navigated primary THA with data collected retrospectively from 2005 to 2010 (64 classic Hardinge approach (HAL) and 66 MIS intermuscular anterolateral approach by the senior surgeon). Data include: operative time, perioperative bleeding, length of surgery, hospital stay, patient's satisfaction and pain perception. The alignment values at six months to a maximum of 60 months provided necessary statistical information for clinical and radiological comparison of the two groups.

Significant differences were found between the two groups with MIS being superior with respect to less surgical time (p = 0.029) and achieving quicker rehab goals with shorter hospital stay (p <0.001). Pain perception was less in MIS group with a higher satisfaction score (p <0.001). Although both groups have the potential of nerve injury to tensor fascia muscle, it's only the classic HAL that jeopardises the glutei nerve supply.

MIS approach to navigated THA seems to be an acceptable alternative with some advantages to Classic HAL.

Proximal load fixation in THA is paramount for maximum bone preservation and thus longevity of the implant. Conventional femoral stems may not achieve satisfactory proximal fixation in proximal/ distal femoral canal mismatch as in champagne type of femur, mal-united fractures, excessively bowed femur and some young large patients. Such mismatch can lead to uneven loading and a higher incidence of loosening or periprosthetic fracture. This risk is becoming higher with the recent trend to mini-invasive surgery. As an alternative to standard stem, the short stem femoral prosthesis was originally developed in the 1950’s and has recently been making a resurgence as a design conducive to the minimal invasive techniques, and allows for greater preservation of the natural anatomy. Our objective is to measure the clinical and radiological outcomes of the Metha^® hip short stem (a cementless, metaphyseal fix conserving diaphysis implant) with computer assisted technique and minimal invasive surgical approach.

This study is a single center, open label, data collection study of 35 consecutive subjects undergoing OrthoPilot^® navigation, Metha^® stem plasmapore cup system with minimal invasive muscle sparing surgical approach. (B. Braun Aesculap; Tuttlingen, Germany). Pre-Operatively an IRB Informed Consent, no exclusion specific to the implant, Harris Hip Evaluation and routine hip/pelvis plain xray was performed. Post-Operatively, a CT Scan within 6 months, repeat Harris Hip Score (HHS) Evaluation. The implant is made of titanium alloy with plasmapore coating in @ 2/3 of the implant (< 8 cm engages in proximal femur with a total length average of 10.75 cm)(range 9.75–11.75). The bearing surface is metal/ highly cross linked polyethylene. Size 32 head of modular neck with plasmapore shell. All cases were done thru muscle sparing anterolateral mini invasive approach.

At 6 months ± 1 month with an average age = 67, BMI= 37 (one was 360 pounds), Harris score was 46 preop and 96 post op.No thigh pain, No dislocation, Trendelenberg negative. Patient satisfaction was high. One fell had a non displaced fx of the neck that did not require revision but slowed full weight bearing for 6 weeks. One subsided in a 360 pound patient after he went full wt bearing while getting out of the shower a week after surgery. This was revised with a standard stem. The tip of two implants was discovered to have penetrated the proximal femur with no symptoms at 3 months period and no restriction to weight bearing during that period. This happened in the first 5 cases in which we modified technique with no other penetrations. Xray/CT scan showed no subsidence good bony ingrowth no radiolucency or loosening. The two penetrated corteses showed intense bony overgrowth on the two protruded tips of stem.

We conclude that cementless metaphyseal short stem with proximal plasmapore coating is associated with excellent clinical and radiological results. The technical errors we faced in the early two cases were identified and avoided by using awl canal finder with suction tube palpation of canal and direct visualization of the metaphyses before hammering the broach. The combination of the short stem prosthesis, modularity of the neck, computer assisted technique and minimal invasive arthroplasty is expected to reduce recovery time, increase the potential for successful restoration of function and add to the longevity of the prosthetic joint.

There is a significant variation in registering anterior pelvic plane (APP) among experienced navigated hip surgeons reflecting negatively on the accuracy of determining the inclination and anteversion angles. Registering the APP in a lateral decubitus position is more challenging in obese patients as palpation of pubic tubercle or anterior superior iliac spines (ASIS) is inconsistent. We propose an alternative and easier novel method in which palpation of the posts (pegs) that stabilizes the pelvis will accurately determine the APP plane. The computer data obtained from peg’s palpation was compared to data obtained from post-operative CT scan of the pelvis in determining acetabular and cup version and inclination angles.

The APP was defined and registered in 40 navigated total hip arthroplasty (THA) patients using our novel method. The patient is securely stabilized in a lateral decubitus position as routine with multiple pegs. One peg is positioned against both ASIS with 2 EKG pads placed on the pegs (each represent an ASIS). The other peg supports the pubic symphysis with one EKG pad representing the pubic tubercle. All efforts are made to make sure that the distance between the EKG nipples and the corresponding ASIS or pubic tubercle is equal before scrubbing and draping of the hip. Registration is achieved afterwards, by touching the nipples of the EKG pads placed on the pegs through the drape while the patient is secured in lateral decubitus position. This way sterility is uncompromised. To test the validity of our method of identifying the APP plane, a post-operative CT scan measurements of cup inclination and version angles were independently observed and the data were compared to our navigation registration method using t-student test analysis.(p=0.05 is significant)

The mean CT-scan cup version was 19.4(S.D. ±6.3), and the mean of APP navigated cup version was 14.2(S. D.±3.1). There was no statistical significant difference (p=0.045). Similarly, there was no significant difference between mean CT scan cup inclination angle of 42.3(S. D.±3.7) and the mean navigated cup inclination of 40.9(S.D.± 4.6), (p= 0.69). Therefore, we conclude that the APP plane can be registered reliably and accurately by simply touching the EKG pads on the pegs and through the drapes. Not to mention, both the cup version and inclination angles were within safety zone of Lewinick.

It seems that the accuracy of measuring the inclination angle through our method, although not significant, is better than the accuracy of measuring the cup version. This emphasizes the point that identifying the pubic tubercle is difficult whichever method of registration is used. However, inaccessibility of ASIS or pubic tubercle during manual APP registration leads to great cup orientation inaccuracies. The readily palpable EKG nipples on the pegs, irrespective of patient’s weight or the thickness of surgical draping, makes this novel technique a reliable and an easier alternative registration method than the manual palpation of APP in navigated THA.

The purpose of mini-invasive hip arthroplasty is least damage to skin and muscles. Unlike Roettinger modification to Watson-Jones, our approach requires no special table or instruments. Besides, direction of skin incision is perpendicular to interval between glutei and tensor muscles, thus called a Crisscross Approach. Potentially, a cross shape exposure allows a larger view and therefore a lesser damage to skin and muscles during retraction. Skin incision, being in line with the femur (almost parallel), allows expansion of incision proximally and distally. No tendon or muscles are severed achieving a true inter-muscular minimally invasive approach.

After working with 3 cadavers to perfect the technique and with investigation and research board (IRB) approved consent, 40 prospective patients underwent mini-invasive crisscross technique from December 06–June 07 with 6 months follow up. A standard non-cemented hip was implanted. Previously disrupted hip muscles patients were excluded. Patients were positioned in a lateral decubitus with pelvis secured and flexed 20°–30°. Incision started 2 inches inferior and posterior to ipsilateral anterior superior iliac spine (ASIS) extending distally for 3 inches or more for obese or muscular patients. Acetabulum is exposed using curved Hohmann retractors one above and one below femoral neck after excising most of the anterior capsule with releasing the superior and inferior capsule. The femoral neck is osteotomised as routine extracting the femoral head. Then the same curved retractors are placed behind anterior and posterior rim of acetabulum with an optional third curved retractor may be placed at the inferior rim. The acetabulum is reamed with the usual straight reamers and the cup is then implanted as routine. Angled reamers are not necessary as our skin incision is in line with the reamer direction. Femoral neck exposure starts with the surgeon positioned anterior to pelvis. Paralysis of the muscles is confirmed with anesthesiologist and table is tilted 20°–30° posteriorly. Hip is then extended 20°–30°, externally rotated to 80°–90° and adducted with a retractor underneath femoral neck. Another curved retractor is placed gently on greater trochanter to protect glutei. Leg is allowed to drop in a bag. Canal finder and use of box osteotome is helpful to avoid breaching the femoral cortex or varus positioning of the stem. Broaching or reaming and final implant insertion is done as routine. Hip reduction is achieved as routine by reversing the table tilt and bringing the leg forward with traction and internal rotation.

36 out of 38 eligible patients were sent home after their rehab goals were met in 4 therapy sessions (2–3days). Full weight bearing was allowed in 4 weeks. One stem was undersized, two were in slight varus, and total blood loss was less than 5 gm/dl of Haemoglobin at post op day three. No dislocation or complications related to exposure. No neurovascular injury and no re-operation. Surgery time averaged 20 minutes longer mainly at femoral exposure. As experience is gained the time is lessened. Post-operative intravenous morphine pump administration was stopped in 24 hours in 82% of patients after surgery instead of the 48 hour routine.

Crisscross approach differs by transecting no tendon or muscles, requiring no special table or instruments with incision that gives more exposure, allows expansion and reduces skin damage resulting in true non-invasive approach. Exposure of the femur was difficult in the first few cases. Tilting the operating table posteriorly, releasing superior and inferior capsule as has been recommended by previous authors helped femoral exposure. Recovery from surgery in terms of rehab sessions and postoperative pain control were improved compared to our previous standard of care. Long term follow up is under current research investigation.

Most common complication of non-navigated classic total knee arthroplasty (TKA) relates to patella. Not resurfacing the patella makes exposure more difficult in a mini-approach which may add to its potential complications. Effect of navigated mini sub-vastus TKA on native patella is clinically and radiologically studied, observing also, whether severity of deformity or obesity adds to patellae complications in such approach.

92 of 100 subjects were eligible. Peri-operative radiological and navigation data with follow up visits to 24 months provided alignment, patella tilting or displacement data. Clinical outcome gauged by “KSS” documented pain from patella movements, or pain generated from stair climbing, or rising from a chair. Patella is considered subluxated if it displaced ≥ 5mm. No exclusion by obesity or severity of deformity. Results were evaluated with descriptive statistics.

Of the 92 patients, 3 had patella pain (3%). 72% had < 5° of patella tilting (of which 3 had patella pain) while 28% had a 5°–17° tilting. As for patellae displacement, 12% displaced laterally (≤3 mm) but with no pain. None had patellar displacement ≥ 4mm (which we define as subluxation), and none had a dislocation. Pre-operative knee deformity ranged from 19° varus to 13° of valgus. 70% of subjects had pre-operative varus/valgus deformity of < 10°. The other 30% had deformity of ≥ 10°. Post-operative mean mechanical axis alignment was 0° (± 1°) with a mean range of motion of −3.8° to 133.6°. No vascular injuries, skin necrosis, deep infection, or fractures.

The BMI ranged from 25–46 Kg/m². 16% had a BMI ≥ 40 with no patellar pain, tilting or displacement.

Incidence of native patella pain in a navigated mini sub-vastus TKA was low irrespective to body mass or pre-operative deformity. Perhaps navigation helped align the components ideally and thus reducing the complication rate of a mini-approach. However, 28% of native patella tilted > 5° but unlike tilting of a resurfaced patella, it did not correlate with patella pain. In this study, whether non-resurfacing caused the 3% of patella pain is undetermined. Nevertheless, the pain level was not severe to make the patients seek a revision of the patella. Finally, as we compare with other studies, we cannot conclude that mini sub-vastus approach is superior; however its low patella complication rate is comparable if not superior to classic approach.

The necessity of soft tissue release to achieve a stable, balanced knee in previous publications has a high rate and a wide range of 50–100% of total knee arthroplasties (TKA). This reflects disagreement regarding the determinants for soft tissue release which is partly due to lack of standardized quantitative measures. Recent advances in navigation may standardize and replace conventional methods regarding soft tissue balancing. We propose two navigation predictors that quantitatively determine the least amount of collateral ligament release necessary to achieve a stable neutral knee, thus reducing the frequency of release.

100 patients underwent navigated TKA. Data of 93 were eligible. Preoperative deformity ranged 18°varus −13° valgus. Ratio of Varus/Valgus= 66/27. Ages were 46–85 yrs. Mean BMI= 36Kg/m²

First navigation predictor determines collateral release when varus/valgus deformity is uncorrectable by stress deflection test before tibia resection. Second predictor determines release when delta mediolateral gap > 4mm before femoral resection using a Tensioner with two independent pads.

10 out of 93 cases (10.75 %), required collateral ligament release to achieve a postoperative mechanical axis of 0° (SE±0.11) with a mean mediolateral deflection in extension of 1.43°, and a mean range of motion of −3° to 127° of flexion. First predictor has 98% accuracy. Second predictor has 96% accuracy but their combination had 100% accuracy with no false negative predictions.

Balanced neutral TKA is achieved by soft tissue release, bone resection or as in this study, by adjusted navigated femoral resection (through rotation, size and level of resection) which balanced knees that otherwise should have soft tissue release. Navigation predictors are reliably accurate to quantitatively determine the necessity of soft tissue release to achieve a neutral stable knee with a significantly lower release rate in comparison to non navigated TKA series rate of 50–100%. (p< 0.001) (95% confidence interval).