Patellar tracking measurement in the normal knee

Eleven fresh frozen cadaveric knee specimens were mounted in a knee kinematics test device, and normal patellar movements were evaluated with use of an external device for direct measurement of patellar movements. The effects of four different measurement conditions were assessed through alteration of one condition and determination of its effect on patellar kinematics with the use of six specimens. The four conditions included (a) change of the measuring axis from an axis parallel to the central axis of the femur (femoral axis) to one parallel to the central axis of the tibia (tibial axis), (b) rotation of the femoral axis internally 6°, (c) change of the direction of the quadriceps force from parallel to the mechanical line of the lower extremity to a direction parallel to the femoral shaft, and (d) increase of the magnitude of the quadriceps force from 111 to 500 N. During knee flexion, the patella shifted laterally after a slight initial medial shift, tilted laterally from midflexion to 90°, and gradually rotated medially. The patellar shift relative to the tibial axis appeared to be more medial than the shift measured relative to the femoral axis; the discrepancy was caused by the valgus position of the tibia relative to the femur. Changing the rotational angle of the femoral axis artifically changed the patellar position. Varying the direction of the quadriceps within the narrow range and increasing the quadriceps force did not affect patellar movements. It is likely that the anatomic configuration of the patella allows the patella to seat in a stable configuration so that it resists moderate changes in the load and direction of the quadriceps. Tibial rotation exerted a major influence on patellar shift and tilt in the early phase of knee flexion: the patella rotated medially when the tibia was externally rotated and rotated laterally when the tibia was internally rotated. These results indicate that the patella may be unstable in the first phase of knee flexion when the tibia is rotated.     

Optimizing patellofemoral tracking during total knee arthroplasty

Fifty-seven patients who underwent 65 primary TKAs between 1993-1994 were retrospectively studied to identify the technical challenges and pitfalls associated with patellar resurfacing and to improve patellar tracking during total knee arthroplasty (TKA). Average patient age was 69 years. All surgeries were performed by a single surgeon (J.N.I), and the same prosthesis was used in all patients. Intraoperatively, attention was paid to avoid femoral and tibial component malrotation and prevent overstuffing of the patellofemoral joint. Preoperative limb alignment was varus in 42 knees, neutral in 6 knees, and valgus in 17 knees. Average pre-resection patellar thickness measured 23.8 mm and post-resection thickness averaged 21.5 mm. No patella-prosthesis composite was thicker than the native patella. Two (3%) knees required a formal lateral release to improve patellar tracking at surgery. Average follow-up for 53 patients (61 knees) was 5 years. At latest follow-up, 4 (6%) patients reported mild anterior knee pain, 5 (7%) patients reported pain with stairs, and 2 (3%) patients had knee crepitus without pain. No dislocations or recurrent subluxations occurred. No patient required revision surgery for patellofemoral complication. Awareness of the anatomic variability, attention to component rotation, and restoration of the normal patellar height improves patellar tracking and minimizes patellofemoral instability following TKA.     

Patellar resurfacing for patellofemoral arthritis.

Knee pain referable to the patellofemoral articulation is common in the general population. It remains a troubling problem for the orthopedic surgeon. Frequently, initial therapy, involving activity modification, anti-inflammatory medications, and isometric quadriceps strengthening, is successful in relieving symptoms. Surgical intervention is normally reserved for those patients with pain that is resistant to these modalities. Unfortunately, none of the various surgical options has proved to be totally dependable, durable, or reproducible. The results of isolated patellar and patellofemoral resurfacing procedures have been guarded. Patellar resurfacing appears to be most beneficial in younger patients with severe anterior knee pain. These individuals should be clearly warned that there is a relatively high likelihood that they will require additional surgical treatment or patellectomy at a later date. Fortunately, patellar resurfacing does not preclude patellectomy from being easily performed. Patellofemoral resurfacing, however, involves more overall involvement of the knee joint. This makes patellectomy less likely to be a successful salvage procedure. Despite our observations that knees with primary patellofemoral arthritis do not do as well after total knee replacement as those with tibio-femoral arthritis, this procedure remains the best treatment option. The durability and predictability of total knee arthroplasty are well documented. Its results far surpass those reported for isolated resurfacing procedures. With regard to patellar resurfacing as part of total knee arthroplasty, we recommend resurfacing all patellae. The literature, although not conclusive, lends support to this practice. Avoidance of metal-backed patellar components and special attention to technical details should decrease the complications associated with patellar resurfacing in future studies.(ABSTRACT TRUNCATED AT 250 WORDS)     

Patellar height and patellofemoral congruence

Summary The patellar tendon/patella ratio and the patellofemoral congruence was estimated in 118 knees. There was a statistically significant positive correlation between the two measurements, high-riding patella occurring with patellofemoral incongruence.

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Zusammenfassung Das Patellarsehnen/Patella-Verhältnis und die Konkruenz des Femoropatellargelenkes wurden in 118 Knien bestimmt. Es zeigte sich eine statistisch zu sichernde Korrelation zwischen Patellahochstand und Inkonkruenz im Femoropatellargelenk.

     

Patellar height and patellofemoral congruence

The patellar tendon/patella ratio and the patellofemoral congruence was estimated in 118 knees. There was a statistically significant positive correlation between the two measurements, high-riding patella occurring with patellofemoral incongruence.     

Mechanical loads at the knee joint during deep flexion.

There is a lack of fundamental information on the knee biomechanics in deep flexion beyond 90 degrees. In this study, mechanical loads during activities requiring deep flexion were quantified on normal knees from 19 subjects, and compared with those in walking and stair climbing. The deep flexion activities generate larger net quadriceps moments (6.9-13.5% body weight into height) and net posterior forces (58.3-67.8% body weight) than routine ambulatory activities. Moreover, the peak net moments and the net posterior forces were generated between 90 degrees and 150 degrees of flexion. The large moments and forces will result in high stress at high angles of flexion. These loads can influence pathological changes to the joint and are important considerations for reconstructive procedures of the knee. The posterior cruciate ligament should have a substantial role during deep flexion, since there was a large posterior load that must be sustained at the knee. The mechanics of the knee in deep flexion are likely a factor causing problems of posterior instability in current total knee arthroplasty. Thus, it is important to consider the magnitude of the loads at the knee in the treatment of patients that commonly perform deep flexion during activities of daily living.     

全膝关节置换术中髌股轨迹的研究现状

髌股关节并发症是全膝关节置换术后翻修最常见的原因[1],多数表现为髌前痛及髌骨外侧半脱位[2-3],少数表现为髌骨骨折[4]、髌骨撞击综合征[5]、髌骨假体松动等。笔者就全膝关节置换术中髌股轨迹的研究现状综述如下。1解剖与生物力学髌股关节由髌骨关节面与股骨滑车沟及内外侧髁     

Patellar tracking in total knee arthroplasty: inset versus onset design

Patellar components come in onset and inset designs. Kinematic differences between these designs were studied in a cadaver model of closed kinetic chain knee extension. Seven frozen knees were implanted with a standard posterior cruciate-retaining design. Each knee first was tested with the inset design, followed by the onset design in the Oxford Knee Rig. Three-dimensional tracking of the femur, tibia, and patella was performed using an electromagnetic system during active knee extension under load. No statistically significant differences were seen in knee kinematics between the 2 designs. The inset patella tended to shift laterally and tilt laterally more than the onset patella. This difference may be clinically significant.     

Patellar band for patellofemoral disorders: results and indications.

In patellofemoral disorders, some cases respond well to conservative management thus the authors' initial treatment is conservative. The Patellar Band (PB) was reported previously (Nakamura et al., 1987). Since then the indications for the band have been investigated. Sixty four patients treated by the PB without operative treatment were classified into eight groups. The Severity of Dysfunction (SOD) was assessed by three grades. The First Grade is dull pain after walking or running for a long distance, the Second Grade is sharp pain on climbing up and down stairs, the Third Grade is a feeling of insecurity. The grouping was as follows: Group Ia - plica syndrome with first Grade of SOD and Ib with Second Grade of SOD. Group IIa - chondromalacia with First Grade of SOD and IIb with Second Grade of SOD. Group III - maltracking patella with patellar pain on flexion. Group IVa - subluxation or dislocation of patella with no previous history of patellar symptom and IVb - recurrent dislocation. Group V - degenerative change of the patella. The PB has been proved to be most effective in Groups Ia, IIa and IVb although it is beneficial in half the cases in Groups IIb and III. The subluxation of the patella was partially reduced without recurrence of dislocation during sports activity and the feeling of insecurity was relieved by the PB. The overall results were not related to age or activity level of the patient. The indication of the band for painful knees was not clearly determined in this study. In all operated cases, it was effective for postoperative instability after lateral release of the retinaculum.     

The effect of patellar thickness on intraoperative knee flexion and patellar tracking in total knee arthroplasty

We designed a simple IRB-approved study to evaluate the intraoperative effect of patellar thickness on knee flexion and patellar tracking during total knee arthroplasty. Routine PCL-retaining total knee arthroplasty was performed in 31 consecutive knees. With clinical balance and congruent patella tracking established, custom trial patellar components that were thicker than the standard trial by 2-mm increments (2-8 mm) were sequentially placed and trialed. Passive flexion was recorded to the nearest 5 degrees with an intraoperative goniometer and gross mechanics of patellofemoral tracking were visually assessed. On average, passive knee flexion decreased 3 degrees for every 2-mm increment of patellar thickness. Furthermore, for the knee system used in this study, increased patellar thickness had no gross effect on patellar subluxation or tilt.     

Physiological sagittal plane patellar kinematics during dynamic deep knee flexion

Purpose

Lateral radiographic views can be easily taken and have reveal considerable information about the patella. The purpose of this study was to obtain sagittal plane patellar kinematics data through the entire range of knee flexion under weight-bearing conditions.

Methods

Patellar flexion angles relative to the femur and tibia and anterior-posterior and proximal-distal translations of the patella relative to the femur and tibia were measured from 0 to 165° knee flexion in nine healthy knees using dynamic radiographic images.

Results

The patella flexed relative to the femur and tibia by two thirds times and one third times the knee flexion angle, respectively. The patella translated in an arc relative to the femur and tibia as the knee flexed. In early flexion, the superior and centroid points translated anteriorly and then the patella translated posteriorly relative to the femur. All three points of the patella translated posteriorly relative to the tibia during a full range of flexion. An average of four and three millimetres proximal patellar translation relative to the tibia was demonstrated from 0 to 20° and 140 to 160° knee flexion, respectively.

Conclusions

Physiological sagittal plane patellar kinematics, including patellar flexion angles and translations relative to the femur and tibia, showed generally similar patterns for each subject. Measurements of dynamic radiographic images under weight-bearing activities may enhance the opportunity to identify patellar pathological conditions.     

Fluoroscopic analysis of knee arthroplasty kinematics during deep flexion kneeling

Achieving deep knee flexion >145 degrees is a goal of many patients receiving knee arthroplasty in Asia and the Middle East, yet it is unknown whether knees with implants move similar to the natural knee in these postures. We studied 18 of 36 consecutively operated knees that were able to flex >145 degrees using fluoroscopic analysis during kneeling to maximum flexion. An average of 9 degrees tibial internal rotation was observed in deep flexion. Posterior condylar translations were observed from 80 degrees to 120 degrees flexion, and the condyles translated forward in flexion beyond 120 degrees. Separation of the condyles from the tibial surface was observed in 9 knees at flexion >130 degrees. Very deep flexion can be achieved and is well accommodated using contemporary posterior-stabilized knee arthroplasty, but the kinematics differ from the intact natural knee.     

Injuries produced by blunt trauma to the human patellofemoral joint vary with flexion angle of the knee.

Patellofemoral joint impact trauma during car accidents, sporting activities, and falls can produce acute gross fracture of bone, microfracture of bone, and soft tissue injury. Field studies of car accidents, however, show that most patellofemoral traumas are classified as 'subfracture' level injuries. While experimental studies have shown that the influence of flexion angle at impact is not well understood, flexion angle may influence injury location and severity. In the current study, 18 pairs of isolated human cadaver knees were subjected to blunt impact at flexion angles of 60 degrees, 90 degrees, or 120 degrees. One knee from each cadaver was sequentially impacted until gross fracture of bone was produced. The contralateral knee was subjected to a single, subfracture impact at 45% of the impact energy producing fracture in the first knee. The fracture experiments produced gross fracture of the patella and femoral condyles with the fracture plane positioned largely within the region of patellofemoral contact. The fracture location and character changed with flexion angle: at higher flexion angles the proximal pole of the patella and the femoral condyles were more susceptible to injury. For the 90 degrees flexion angle, the patella was fractured centrally, while at 60 degrees the distal pole fractured transversely at the insertion of the patellar tendon. In addition, the load magnitude required to produce fracture increased with flexion angle. In the 'subfracture' knees, injuries were documented for all flexion angles; occult microfractures of the subchondral and trabecular bone and fissures of the articular surface. Similar to the fracture-level experiments, the injuries coincided with the patellofemoral contact region. These data show that knee flexion angle plays an important role in impact related knee trauma. Such data may be useful in the clinical setting, as well as in the design of injury prevention strategies.     

全膝关节置换术中股骨假体屈曲对髌股关节生物力学影响的实验研究

[目的]探讨全膝置换术中股骨假体矢状位上屈曲对髌股关节生物力学的影响,为临床指导人工膝关节置换的手术技术提供实验依据,以减少术后髌股关节的并发症。[方法]取正常国人新鲜冷冻尸体的5个膝关节作为研究对象,模拟膝关节自站立位屈膝下蹲的动作,设计制作膝关节实验架,与生物力学测试仪共同搭建实验平台。人工膝关节采用DePuy PFC假体全膝系统,手术由同一位有经验的术者实施以控制实验误差,置换髌骨。比较股骨假体相对于按下肢力线位、前屈5°、10°及后屈5°、10°、15°位置时的髌股关节的生物力学指标。选择屈膝30°、60°、90°、120°为观察角度,采用美国Tecscan公司生产的感测片测定髌股关节接触压峰值,最后软件处理得到数字化的结果。[结果]除了在膝关节屈曲30°、60°、90°,股骨假体前屈5°时,髌股关节内侧间隙接触压峰值与下肢力线位相比较无显著性差异(P>0.05),其余各种屈膝角度下,股骨假体不同屈曲角度所致髌股关节内外侧间隙接触压峰值与下肢力线位比较有显著性差异(P<0.05)。股骨假体后屈角度越大,峰值的升高越明显。[结论]全膝关节置换术中,股骨假体在矢状位上争取按下肢力线位置入,以降低术后并发症的发生。     

The effect of surgical approaches and tourniquet application on patellofemoral tracking in total knee arthroplasty

The purpose of this study was to assess the influences of surgical approaches and tourniquet application on the lateral retinacular tension (LRT). Single-setting bilateral total knee arthroplasty was performed in 10 patients, and the medial parapatellar and midvastus approaches were randomly performed on each knee using tourniquet application. The LRT was measured using the buckle transducer before and after each approach. Next, the tourniquet was deflated and the measurement was repeated. After the parapatellar approach, LRT was significantly decreased. Conversely, no significant change was seen after the midvastus approach with the tourniquet inflated. However, in the midvastus approach, LRT was significantly decreased after tourniquet deflation. We concluded that both the parapatellar and midvastus approaches influence patellar tracking and LRT.     

The effect of a tourniquet on intraoperative patellofemoral tracking during total knee arthroplasty

A prospective investigation was performed on the effect of the tourniquet on intraoperative patellofemoral tracking during primary total knee arthroplasty (TKA). A total of 75 TKAs in 67 patients were performed by 1 surgeon in a consecutive series using the same technique. Using strict criteria, patellar tracking was assessed both before and after tourniquet release. Patients were placed into 1 of 3 groups: Group I were knees that tracked properly both before and after tourniquet release. Group II were knees that maltracked with the tourniquet inflated and subsequently corrected with the tourniquet released. Group III were knees that maltracked both before and after tourniquet release, therefore requiring a lateral release. Knees were categorized as group I, 34 of 75 (45.3%); group II, 36 of 75 (48.0%); and group III, 5 of 75 (6.7%). Using this criterion, lateral release was avoided in all group II knees. Tourniquet application alters intraoperative patellofemoral tracking during TKA. When contemplating lateral release, tourniquet deflation and reevaluation of patellofemoral tracking should be considered.     

In vivo knee kinematics during stair and deep flexion activities in patients with bicruciate substituting total knee arthroplasty

Orthopedic surgeons and their patients continue to seek better functional outcomes after total knee arthroplasty. The bicruciate substituting (BCS) total knee arthroplasty design has been introduced to achieve more natural knee mechanics. The purpose of this study was to characterize kinematics in knees with BCS arthroplasty during deep flexion and stair activities using fluoroscopy and model-image registration. In 20 patients with 25 BCS knees, we observed average implant flexion of 128° during kneeling and consistent posterior condylar translations with knee flexion. Tibial rotations were qualitatively similar to those observed in the arthritic natural knee. Knee kinematics with BCS arthroplasty were qualitatively more similar to arthritic natural knees than knees with either posterior cruciate-retaining or posterior-stabilized arthroplasty.     

Three-dimensional tibiofemoral kinematics during deep flexion kneeling in a mobile-bearing total knee arthroplasty

Achieving very deep flexion after total knee arthroplasty is an important goal of most patients in Japan, Asia, and the Middle East because of floor-sitting lifestyles. Numerous knee arthroplasty designs have been introduced to permit high flexion. We performed an in vivo radiographic analysis of tibiofemoral motions during weight-bearing kneeling in one high-flexion knee arthroplasty design. Twenty knees implanted with a posterior-stabilized rotating-platform knee arthroplasty flexed an average of 126°. The femoral condyles translated posteriorly from extension to maximum flexion. Total posterior condylar translations averaged 11.6 and 4.7 mm for the lateral and medial condyles, respectively. Tibial internal rotation in 19 knees averaged 9° from extension to maximum flexion. Knees implanted with a posterior-stabilized, rotating-platform knee arthroplasty show deep flexion knee kinematics consistent with the implant design intent.     

Patellar resurfacing in total knee arthroplasty. A meta-analysis

BACKGROUND: Patellar resurfacing during total knee arthroplasty remains controversial. We aimed to evaluate the effectiveness of this technique through an evaluation of the current literature. METHODS: We performed a meta-analysis of randomized controlled trials comparing total knee arthroplasties performed with and without patellar resurfacing. Outcomes of interest included the number of reoperations, the prevalence of postoperative anterior knee pain, and the improvement in various knee scores. RESULTS: Ten trials assessing 1223 knees were eligible. The absolute risk of reoperation was reduced by 4.6% (95% confidence interval, 1.9% to 7.3%) in the patellar resurfacing arm (between-study heterogeneity, p < 0.01; I(2) = 60%), implying that one would have to resurface twenty-two patellae (95% confidence interval, fourteen to fifty-two patellae) in order to prevent one reoperation. Patellar resurfacing reduced the absolute risk of postoperative anterior knee pain by 13.8% (95% confidence interval, 6.4% to 21.2%), implying that one would have to resurface seven patellae (95% confidence interval, five to sixteen patellae) in order to prevent one case of postoperative anterior knee pain. Only four trials provided adequate data for a quantitative synthesis of the changes in the various knee scores; on the basis of those four trials, there was no difference in the mean improvement in the knee scores (standardized mean difference, 0.03; 95% confidence interval, -0.50 to 0.56). CONCLUSIONS: The available evidence indicates that patellar resurfacing reduces the risks of reoperation and anterior knee pain after total knee arthroplasty. The observed effects are clinically important despite their modest magnitude. Additional, carefully designed randomized trials are required to strengthen this claim.