高位髌骨：何时矫正及对髌股不稳定的其他解剖学危险因素的影响 (2022)

高位髌骨：何时矫正及对髌股不稳定的其他解剖学危险因素的影响 (2022)Patella Alta: When to Correct and Impact on Other Anatomic Risk Factors for Patellofemoral Instability

Biedert R M. Patella Alta: When to Correct and Impact on Other Anatomic Risk Factors for Patellofemoral Instability[J]. Clin Sports Med, 2022,41(1): 65-76.

转载文章的原链接1：

https://pubmed.ncbi.nlm.nih.gov/34782076/

转载文章的原链接2：

https://www.sportsmed.theclinics.com/article/S0278-5919(21)00056-9/fulltext

Abstract

Patella alta is described as abnormally high-riding patella in relation to the femur, the trochlear groove, or the tibia with decreased bony stability. Patella alta represents an important predisposing factor for patellofemoral instability. Different measurement methods are used to define patella alta. Despite the clinical importance of patella alta, there is only limited consensus on cutoff values, indications for treatment, and ideal correction. In addition, the impact of patella alta on other risk factors for lateral patellar instability is significant. This must be considered when assessing clinical complaints and choosing the best individual treatment. Combined surgical interventions may be necessary.

高位髌骨被描述为与股骨、滑车沟或胫骨相关的异常高位髌骨，并伴有骨稳定性下降。高位髌骨是髌股不稳的重要易感因素。不同的测量方法用于定义高位髌骨。尽管高位髌骨具有重要的临床意义，但在截断值、治疗指征和理想矫正方面的共识有限。此外，高位髌骨对外侧髌骨不稳定的其他危险因素的影响是显著的。在评估临床主诉和选择最佳个体治疗时必须考虑到这一点。联合手术干预可能是必要的。

Keywords: Distalization; Osteotomies; Patella alta; Patellofemoral instability; Rotational abnormalities; Treatment; Trochlear dysplasia.

KEY POINTS

Ø Patella alta has a decreased patellotrochlear cartilage overlap and represents a predisposing factor for symptomatic patellofemoral instability.

Ø Patella alta is defined as CDI greater than 1.2, ISI greater than 1.3, and PTI less than 0.125 to 0.28.

Ø Indications for surgical correction are mostly based on the CDI (＞1.2) and the PTI (＜0.125–0.28).

Ø The desired postoperative patellar height is CDI of 1.0 to 1.2, PTI of 0.3 to 0.4, and ISI of 0.95.

Ø Patella alta has a strong impact on other risk factors for patellofemoral instability and vice versa.

Ø 高位髌骨会降低髌股关节软骨的重叠程度，是出现症状性髌股不稳定的危险因素。

Ø 髌骨高位症的定义是CDI大于1.2、ISI大于1.3、PTI小于0.125至0.28。

Ø 手术矫正的指征通常基于CDI（大于1.2）和PTI（小于0.125至0.28）。

Ø 理想的术后髌骨高度是CDI为1.0至1.2、PTI为0.3至0.4、ISI为0.95。

Ø 高位髌骨对其他髌股不稳定的危险因素以及这些因素对高位髌骨的影响都很大。

INTRODUCTION

Different morphologic abnormalities, such as patella alta, trochlear dysplasia, rotational abnormalities, excessive tibial tubercle-trochlear groove (TT-TG) distance, patellar tilt, and hypermobility, are predisposing factors for symptomatic patellofemoral (PF) instability.1–5 They are present alone or in variable combinations and differently affect patellar kinematics.6 A precise assessment of the pathologic anatomy and modified biomechanics of PF instability is therefore essential for improved understanding of the altered forces acting on the axial, coronal, and sagittal plane and for optimal treatment. Considering this, individually tailored surgical correction may be necessary for successful outcomes in patients with long-term complaints and failed conservative treatment.

不同的形态异常，如高位髌骨、滑车发育不良、旋转异常、胫骨结节-滑车沟(TT-TG)距离过大、髌骨倾斜和活动过度，是症状性髌骨股骨(PF)不稳定的易感因素。它们单独存在或以可变组合存在，不同程度地影响髌骨运动学因此，对PF不稳定的病理解剖和改良的生物力学进行精确评估对于提高对作用在轴、冠状面和矢状面上的改变力的理解和最佳治疗是必不可少的。考虑到这一点，对于长期抱怨和保守治疗失败的患者来说，个体化的手术矫正可能是必要的。

Patella alta is described as abnormally high-riding patella in relation to the femur, the TG, or the tibia with decreased bony stability.7–11 Typically, patella alta has a reduced articular area of PF contact with decreased patellotrochlear cartilage overlap.1,12–14 Sometimes the patella sits even out of the trochlea, especially with quadriceps muscle contracted, and is associated with increased lateral translation.14 An abnormally high positioned patella may therefore insufficiently engage the proximal TG in extension and early knee flexion. Accordingly, patella alta is one of the potential risk factors for PF instability.5,10,15–17 In addition, it is also observed in patients with PF pain, chondromalacia, Sinding-Larsen-Johansson disease, Osgood-Schlatter disease, patellar tendinopathy, and osteoarthritis representing also an important predisposing factor for patellar malalignment and PF-related complaints.1,6,7,13,16,18,19 In contrast, patella alta may also be a normal variant of individual knee anatomy and is well tolerated without additional instability factors.5

高位髌骨被描述为与股骨、TG或胫骨相关的异常高位髌骨，并伴有骨稳定性下降7-11。典型的情况是，髌骨上有PF接触的关节面积减少，髌滑车软骨重叠减少1,12 - 14。有时髌骨甚至位于滑车之外，特别是在股四头肌收缩时，并与外侧平移增加有关异常高位的髌骨。因此，可能在膝关节伸展和早期屈曲时不能充分接合近端TG。因此，高位髌骨是PF不稳定的潜在危险因素之一5,10,15 - 1。7此外，在PF疼痛、软骨软化症、Sinding-Larsen-Johansson病、osgood - schlate病、髌骨肌腱病和骨关节炎患者中也可以观察到，这也是髌骨错位和PF相关疾病的重要易感因素1、6、7、13、16、18、19。相反，高位髌骨也可能是单个膝关节解剖结构的正常变体，并且在没有额外不稳定因素的情况下耐受性良好。

In the normal knee, the patella enhances functionally the lever arm of the extensor mechanism.20 During the range of motion, high loads transfer to the articular side of the patella. The contact point changes between patella and trochlea during flexion-extension movements and the joint reaction forces (JRF) change because of altered force vectors in the lever system.20 The thick articular cartilage of the patella dissipates large JRF during contractions of the quadriceps muscle.

在正常的膝关节中，髌骨在功能上增强了伸肌机制的杠杆臂在活动范围内，高负荷转移到髌骨关节侧。在屈伸运动中，髌骨和滑车之间的接触点发生变化，关节反作用力(JRF)也因杠杆系统中力矢量的改变而发生变化髌骨的厚关节软骨在股四头肌收缩时消散大JRF。

In patients with patella alta, joint kinematics and cartilage contact position are altered caused by a modified lever arm between quadriceps and patellar tendon.21 Patella alta is correlated with a larger quadriceps and smaller patellar tendon moment arm with a greater transmission force from quadriceps to patellar tendon.16,22 A posteriorly directed force on the patella is generated by the altered pulls of the quadriceps tendon and the patellar tendon and supraphysiologic lateral force vectors can result.20 The altered position of the patella may lead to elevated PF joint contact stress because of smaller contact area and increased JRF in deeper knee flexion resulting in cartilage damage, PF pain, or complaints.14,23

在高位髌骨患者中，在股四头肌和髌骨肌腱之间安装改良的杠杆臂会改变关节的运动学和软骨接触位置髌骨上缘与股四头肌较大、髌骨肌腱力矩臂较小相关，股四头肌到髌骨肌腱的传递力较大16,22。髌骨上的后向力是由股四头肌肌腱和髌骨肌腱拉力的改变和生理上的侧向力矢量产生的髌骨位置的改变可能导致PF关节接触应力升高，因为较小的接触面积和更深的膝关节屈曲中增加的JRF导致软骨损伤，PF疼痛或抱怨。

MEASUREMENT METHODS

Overall, four different types of measurement methods are used to assess patella alta: (1) lateral radiographs with corresponding ratios, (2) radiograph ratios measured on MRI, (3) patellotrochlear index (PTI) on sagittal MRI, and (4) patellar tendon length measurement.1 The cutoff values for patella alta according to the specific measurement method are summarized in Box 1.1,10,12,24 However, there is still no generally accepted consensus for any measurement method or cutoff value for patella alta.

总的来说，四种不同类型的测量方法被用于评估髌骨上缘:(1)侧位x线片相应的比例，(2)MRI X线片测量的比例，(3)矢状面MRI髌骨滑车指数(PTI)，以及(4)髌骨肌腱长度测量根据具体测量方法对髌骨上切值的总结见Box 1.1、10、12、24。然而，对于任何一种测量方法或cutoff value，目前仍没有普遍接受的共识。

Box 1 Measurement methods for patella alta with cutoff values

Radiograph measurements

Caton-Deschamps index ＞1.2

Insall-Salvati index ＞1.3

Blackburne-Peel index ＞1.0

Radiograph ratios on sagittal MRI sequences

Caton-Deschamps index ＞1.2

Insall-Salvati index ＞1.3

Sagittal MRI (central cut)

PTI ＜0.125–0.28

Sagittal MRI (longest patella axis)

Patellar tendon length (Insall-Salvati index) ＞52 mm

The radiograph measurement indices mark the position of the patella relative to the tibia.1,12 The variable bony morphologies of patella (distal patella nose, different articulating surface, fragmentation distal patellar bone), femoral trochlea (facet in length and height), proximal tibia (TT deformities, fragmentation, hypertrophy), and slope are confounding factors that may affect measurement.1 Specific variations in PF morphology (eg, small articular surface, short trochlea) are not represented by these indices. Therefore, correct measurement for patella alta should preferably relate the position of the patella to the femur rather than the tibia.25

X线测量指标标记髌骨相对于胫骨的位置1,12。髌骨的不同骨形态(远端髌骨nose、不同关节面、远端髌骨碎裂)、股滑车(关节面长度和高度)、胫骨近端(TT畸形、碎裂、肥大)和坡度是可能影响测量的混杂因素。PF形态的具体变化(如关节面小，滑车短)不能用这些指标来表示。因此，正确测量上髌骨的位置最好是髌骨与股骨的位置，而不是胫骨的位置

In addition, the real articular PF relationship is not sufficiently assessed because articular cartilage is not visible on radiographs (Fig. 1).1,12,19 The cartilaginous overlap between trochlea and patella represents the most relevant factor for patella alta and should be measured using MRI.5,10,12,19 Therefore, the use of the PTI is recommended for precise assessment (Fig. 2). The PTI traces preoperative and postoperative values, which makes these measurements valuable.

此外，真正的关节PF关系没有得到充分评估，因为关节软骨在X线片上不可见(图1) 1,12,19。滑车和髌骨之间的软骨重叠是导致髌骨高位的最相关因素，应该使用MRI进行测量5,10,12,19。因此，建议使用PTI进行精确评估(图2)。PTI记录了术前和术后的值，这使得这些测量值很有价值。

Fig. 1. Lateral radiograph shows patella alta. The cartilaginous overlap between trochlea and patella is not visible.

Fig. 2. Patellotrochlear index measured on sagittal MRI (central cut) shows the missing true articular patella (dotted line), and trochlea (solid line) overlap in patella alta with impingement of the Hoffa fat pad.

Using radiograph measurements only, the Caton-Deschamps index (CDI) is superior to the Insall-Salvati index (ISI), especially when considering surgical correction with distalization of the TT.1

The CDI assesses the height of the patella relative to the tibial plateau and is therefore the most useful measuring method on radiographs for patellar height before and after distalization of the TT.1 The ISI does not change after distalization of the TT and therefore cannot be recommended.1

CORRECTION OF PATELLA ALTA

Treatment of patella alta is conservative at the beginning. The focus is on improved functional stability, coordination, and strength. The patella is externally stabilized using kinesiotape or soft brace to reduce symptoms during practice.

Surgical correction of patella alta is indicated in patients with a long history of ongoing symptoms, unsuccessful conservative treatment over a long period, functional disability, clinical examination findings, and documentation by imaging. The ideal surgical procedure to address patella alta should restore biomechanics of the extensor mechanism of the knee and increase PF stability.23 In addition, PF joint contact stress and JRF should normalize. The appropriate procedure depends on the patient’s anatomy, pathomorphology, and age. Various combinations are used to address all causes of instability or complaints.

高位髌骨手术矫正适用于有长期持续症状、长期保守治疗不成功、功能残疾、临床检查结果和影像学记录的患者。治疗高位髌骨的理想手术方法应该是恢复膝关节伸肌机制的生物力学，并增加膝前关节的稳定性。此外，PF接头接触应力和JRF应正态化。适当的手术取决于病人的解剖结构、病理形态和年龄。使用各种组合来解决不稳定或主诉的所有原因。

Indications by Measurements

The different surgical procedures to correct patella alta are primarily based on the CDI and the PTI,1,10 more rarely on the ISI (Table 1).

矫正高位髌骨的不同手术方法主要基于CDI和PTI，很少基于ISI(表1)。

Table 1 Indications to treat patella alta

Surgical Procedures

Two types of surgical procedures are used to correct patella alta: TT osteotomies and soft tissue methods.

Transfers of the tibial tubercle

TT distalization is an effective procedure of normalizing patellar height to correct the patellar index in patella alta.1,18,27,31,32 TT distalization is indicated in patients with recurrent patellar dislocations, PF pain, Hoffa impingement, and cartilage lesions because of patella alta and facilitates the engagement with the TG at low flexion angles.1,3,8 It is performed as a single procedure or in combination with other stabilizing interventions. Additional medialization or anteromedialization may be indicated in cases with increased TT-TG distance (＞20 mm), cartilage lesions, or osteoarthritis.TT osteotomy is performed in two planes: three-dimensional or V-shaped.13

TT远端化术是矫正髌骨上趾髌骨指数的有效方法1,18,27,31,32。由于高位髌骨导致复发性髌骨脱位、PF疼痛、Hoffa撞击和软骨病变的患者适用于TT远端化，以促进低屈曲角度与TG的接合1,3,8。它可以作为一个单一的程序或与其他稳定干预相结合。在TT-TG距离增加(＞ 20mm)、软骨病变或骨关节炎的病例中，可能需要额外的内侧化或前内侧化。TT截骨术在两个平面上进行:三维或V形。

The patellar height, TT-TG distance, and lateral patellar subluxation improve after surgery depending on the amount of correction. Posteriorization must be strictly prevented in order not to increase PF contact forces. Direction and degree of TT transfer must be individually adapted preoperatively according to patient parameters and focus on the goal of the procedure.33 The amount of the desired distalization is calculated to result in a postoperative CDI of 1.0 to 1.2, and PTI of 0.3 to 0.4 (Table 2, Fig. 3).1,20

术后髌骨高度、TT-TG距离和外侧髌骨半脱位的改善取决于矫正量。为了不增加PF接触力，必须严格防止后置。术前TT转移的方向和程度必须根据患者的参数单独调整，并关注手术的目标计算所需远距量，术后CDI为1.0至1.2,PTI为0.3至0.4(表2，图3)

Table 2 Desired postoperative patellar height

Fig. 3. Lateral radiograph shows patellar height after distalization of the tibial tubercle. The distally removed bone block is inserted proximally to stabilize the TT osteotomy. The CDI is 1.0.

The risk of complications following TT osteotomies, such as nonunion, tibial fractures, overcorrection, posteriorization, skin necrosis, infection, and hardware complications/irritation, is related to the technique used and is between 3.3% and 10.7%.35

TT截骨术后并发症的风险，如骨不连、胫骨骨折、矫直过度、后置、皮肤坏死、感染和内固定物并发症/刺激，与所使用的技术有关，在3.3%至10.7%之间。

TT distalization and additional patellar tendon tenodesis attached to its original insertion results in normalization of patellar tendon length and a stable PF joint in patients with patella alta.34 Comparing these surgical procedures, cartilage stress seems lower using distalization as opposed to distalization and tenodesis.

TT远端化和附加的髌腱固定在其原始插入处，可使髌腱长度恢复正常，并使髌骨高位患者的PF关节稳定34。比较这些外科手术，与远端固定和肌腱固定术相比，远端固定的软骨应力似乎更低。

Soft tissue methods

Patellar tendon imbrication is an effective procedure to correct patella alta in the skeletally immature patient suffering from lateral patellar instability. Soft tissue methods are recommended because bony procedures injure the proximal tibial physis and may lead to its premature closure.36 On average, this technique allows 1 cm of patellar tendon shortening.

36. Patel R, Gombosh M, Polster J, et al. Patellar tendon imbrication is a safe and efficacious technique to shorten the patellar tendon in patients with patella alta. Orthop J Sports Med 2020;27(8). 2325967120959318.

髌骨肌腱imbrication是一种有效的手术，以纠正髌骨外侧不稳定的骨未成熟患者的髌骨上翘。推荐使用软组织法，因为骨性手术会损伤胫骨近端，并可能导致其过早闭合。平均而言，该技术可使髌腱缩短1厘米。

Distal advancement of the patella can also be achieved by complete mobilization of the patellar tendon and fixed with sutures through the cartilaginous TT. This technique offers a satisfactory treatment of the immature patient presenting with habitual patellar dislocation associated with patella alta.37

37. Biedert RM, Netzer P, Gal I, et al. The lateral condyle index: a new index for assessing the length of the lateral articular trochlea as predisposing factor for patellar instability. Int Orthop 2011;35:1327–31.

髌骨远端化也可以通过髌骨肌腱的完全活动和通过软骨TT缝合固定来实现。这项技术对表现为习惯性髌骨脱位并高位髌骨的未成熟患者提供了满意的治疗。

IMPACT ON OTHER ANATOMIC RISK FACTORS

Patella alta may also be present in combination with other risk factors for patellar instability. The variable combinations of deformities affect patellar kinematics in different ways.6 Therefore, the impacts on the specific risk factors for patellar instability must be assessed to determine the best treatment.

高位髌骨也可能与其他导致髌骨不稳定的危险因素同时存在。畸形的不同组合以不同的方式影响髌骨的运动学。因此，必须评估对髌骨不稳定的特定危险因素的影响，以确定最佳治疗方案。

Anatomic Risk Factors

Trochlear dysplasia

Trochlear dysplasia is an abnormality of shape and depth of the TG with variable length of the articular zone.3,5,17,37 Different forms of trochlear dysplasia are described, such as decreased depth, decreased inclination of the lateral facet, flat trochlea, trochlear bump (anterior translation of the trochlear floor), and hypoplasia of the medial trochlea. These forms of trochlear variations are located proximally and cause decreased bony stability in the TG. The patella is insufficiently guided at the entrance into the trochlea in extension and at the beginning of knee flexion and lateral instability with increased lateral tilt may occur.

Patella alta and trochlear dysplasia (type C and D) in combination represent a severe pathomorphology with two different instability factors resulting in reduced lateral mechanical joint stability (Fig. 4 A and B).38 TT distalization alone would only correct patellar height, but not significantly improve joint stability because of the dysplastic groove, which fails to provide lateral constraint. The engagement of the patella into the dysplastic sulcus (flat or even prominent anterior bump) would still be prevented in extension and early knee flexion. Therefore, deepening trochleoplasty to establish a concave surface of correct depth, length, and sulcus orientation on the proximal trochlea may be necessary at the same time to improve patellar stability. When performing deepening trochleoplasty it is also possible to reduce the TT-TG distance.4 In some cases, only mild deepening may be necessary at the proximal entrance of the trochlea. With this, the contact area increases and the PF contact pressure decreases.

Fig. 4.

(A)Sagittal MRI showing patella alta (PTI 0.14) and trochlear dysplasia type D with prominent supratrochlear spur.

(B)Postoperative lateral radiograph after distalization of the tibial tubercle showing normal patellar height and after deepening trochleoplasty (same patient as Fig. 4A).

Short lateral trochlear facet

A too short proximal-lateral extension of the articular trochlear facet represents another type of trochlear dysplasia in the coronal plane.37 The patella is well centered in the trochlea under relaxed conditions. Muscular contraction of the extensor mechanism leads to proximalization and lateralization of the patella resulting in dynamic lateral subluxation. The lateral subluxation of the patella is caused by the missing osteochondral opposing force of the too short lateral trochlear facet (Fig. 5). With increasing knee flexion, the patella enters into the more distal and normal part of the TG and becomes therefore more stable. But in combination with patella alta, the lateral patellar instability is significantly increased because of the missing lateral facet contact and already present under relaxed conditions.

Fig. 5. Sagittal MRI showing short anterior lateral trochlear facet (arrow) with no patello-trochlear cartilage overlap and patella alta. The PTI is 0, the CDI is 1.3, and the lateral condyle index is 66%.

TT distalization alone would result in normal patellar height and improved joint stability, but only under relaxed conditions. Therefore, proximal-lateral trochlear lengthening osteotomy is recommended at the same time to improve also the dynamic stability in this combination.4,37

Torsional abnormalities

Torsional abnormalities influence the PF kinematics and cause altered vectors and forces acting on the PF joint.39,40 Increased femoral antetorsion represents a significant etiologic factor causing lateral patellar instability.39–42 The knee joint is pointed internally and the pull on the quadriceps is lateral.40 This increases the lateral trochlea facet compression and may cause lateral patellar instability.

In combination with patella alta, the counterforce against lateral patellar instability is decreased or absent because of the missing lateral facet contact and the instability becomes more significant.

Treating patella alta by distalization would increase patella stability, but only until the failure rate of the medial PF ligament (MPFL) is reached. Combined insufficiency of the MPFL and increased femoral antetorsion (＞25°–30°)may result in symptomatic patellar instability by itself. In combination with patella alta, the instability and secondary effects become worse and combined surgical correction consisting of TT distalization and femoral derotation osteotomy may be considered.

通过远端化修复高位髌骨可以增加髌骨的稳定性，但仅在内侧韧带(MPFL)的失败率达到之前。MPFL功能不全和femoral antetorsion增加(＞25°-30°)可能单独导致有症状的髌骨不稳。合并高位髌骨，不稳定性和继发效应加重，可考虑TT远端和femoral derotation osteotomy联合手术矫正。

Excessive tibial tubercle-trochlear groove distance

A lateral insertion of the patellar tendon on the tibia is considered as one of the main factors of patellar instability. This is quantified as the medial-lateral TT-TG distance. A threshold of 20 mm or more signifies an abnormal value.4,6,17,20 In combination with patella alta, the reduced engagement of the patella with the TG and the increased TT-TG distance result in elevated lateral shift, tilt, and instability of the patella. This typically increases with knee extension because of the tibial external rotation of the screw-home mechanism.43 In addition, the interaction of TT lateralization combined with patella alta significantly increases the amount of anisometry seen in the reconstructed MPFL, with almost 5 mm of mean maximal length change demonstrated with the combination of TT-TG of 25 mm and CDI of 1.4.44 Distalization combined with TT medialization restores the engagement of the patella with the TG and reduces patellar lateral shift. With this, the risk of patellar instability is decreased especially near full extension. Overcorrection to medial and/or posteriorization of the TT must be strictly avoided. The use of the tubercle-sulcus angle assessed in 90° of knee flexion may be helpful.

髌骨肌腱外侧插入胫骨被认为是髌骨不稳定的主要因素之一。这被量化为内侧外侧TT-TG距离。20mm以上为异常值4,6,17,20。与高位髌骨结合，髌骨与TG的结合减少，TT-TG距离增加，导致髌骨侧移、倾斜和不稳定加剧。这种情况通常随着膝关节的伸展而增加，因为胫骨的外旋使螺钉复位此外，TT侧化联合高位髌骨的相互作用显著增加了重建的MPFL的参差量，TT-TG 25 mm和CDI 1.4.44的组合显示了近5 mm的平均最大长度变化，远端化联合TT中缘化恢复了髌骨与TG的接合并减少了髌骨的外侧移位。这样，髌骨不稳定的风险降低，尤其是在完全伸展时。必须严格避免过度矫正到内侧和/或后位。在膝关节屈曲90°时使用tubercle-sulcus angle评估可能会有所帮助。

Valgus knee

Excessive valgus knee alignment determines increased lateral patellar displacement with higher risk of dynamic patellar instability, especially close to extension and during quadriceps contraction. This negative effect is exacerbated by the presence of a patella alta at the same time. In this condition, the laterally pulled patella lays completely above the trochlea without osseous support preventing lateral subluxation or dislocation. This results in a multifactorial lateral patellar instability.

Distalization of patella alta improves the bony support in the TG and decreases patellar instability despite the laterally oriented force vectors given by the valgus knee. In cases with excessive genu valgum, femoral varisation (varus producing) osteotomy may be indicated at the same time.45

Medial patellofemoral ligament insufficiency

The MPFL is the most important static soft tissue provider of passive lateral stability for the patella (50%–60%).46,47 The MPFL acts as a checkrein during the first 30° of knee flexion before the patella engaging the TG.48 In patients with patella alta, the MPFL may be insufficient because of the lateral patellar instability. Patella alta significantly alters MPFL anatomometry.44 A reconstruction performed at Schoettle point (as in patients with normal patellar height) would therefore fail to produce a truly anatomometric MPFL. Proximalization of the femoral attachment site of MPFL reconstruction may be necessary.44 TT distalization alone should not be expected to completely correct the instability and MPFL reconstruction or double-breasting reefing must be added. Poor graft positioning should be strictly avoided because misplaced femoral tunnels dramatically increase maximum contact pressures within the PF joint.48

MPFL是髌骨被动侧位稳定性最重要的静态软组织提供者(50%-60%)46,47。在髌骨与TG接合之前的前30°膝关节屈曲中，MPFL起到了checkrein的作用48。在高位髌骨的患者中，由于外侧髌骨不稳定，MPFL可能不够。高位髌骨显著改变MPFL解剖结构因此，在Schoettle点进行重建(如髌骨高度正常的患者)将无法产生真正解剖意义上的MPFL。近端股骨附着部位重建MPFL可能是必要的，单靠TT远端化不能完全纠正不稳定性，必须增加MPFL重建或双排线reefing。应严格避免不良移植物定位，因为错位的股骨隧道会显著增加PF关节内的最大接触压力。

However, persistent patella alta after MPFL reconstruction results in decreased lateral restraining forces, PF contact area, and increased maximum PF contact pressures, which could explain clinical failures of isolated MPFL reconstruction in the setting of patella alta.48 This underlines the importance of TT distalization in patients with patellar instability and the combination of patella alta and MPFL insufficiency.

然而，在髌骨上突重建后，持续的高位髌骨导致外侧约束力、PF接触面积和最大PF接触压力下降，这可以解释在高位髌骨情况下孤立性MPFL重建的临床失败48。这强调了TT远端化对髌骨不稳定和高位髌骨合并MPFL功能不全患者的重要性。

Hypermobility

In patients with patella alta and hypermobility, the elasticity of the ligaments allows for increased lateral displacement of the patella because the bony stability of the TG is missing at the same time. This phenomenon is increased with quadriceps contraction. Patella hypermobility occurs more frequently in patients with patellar dislocation compared with the general population.14,49 This indicates that soft tissue plays an important role in stabilization of the patella, especially at full knee extension when the patella is superior to the bony restraint of the TG.46

在高位髌骨和活动过度的患者中，韧带的弹性允许髌骨外侧移位增加，因为TG的骨稳定性同时缺失。这种现象随着股四头肌收缩而增加。髌骨脱位患者与一般人群相比，髌骨过度活动更常发生14,49。这表明软组织在髌骨的稳定中起着重要的作用，特别是在膝关节完全伸展时，当髌骨优于TG的骨约束时。

Performing distalization of the patella, the patella enters into the trochlea and becomes more stable. Nevertheless, it is recommended to shorten and double-breast the lax ligaments on the medial side at the same time.

进行髌骨远端化，髌骨进入滑车并变得更加稳定。然而，建议同时缩短和double-breast内侧松弛韧带。

CLINICS CARE POINTS

（1）Different morphologic abnormalities are predisposing factors for patellofemoral instability.

（2）Patella alta with insufficient engagement of the patella in the trochlea is a most important one.

（3）Correct imaging assessment of all patella instability factors is mandatory to determine optimal treatment.

（4）All morphologic, biomechanic, and functional factors must be addressed during surgical correction for successful outcome.

(1)不同的形态学异常是髌股不稳定的危险因素。

(2) 高位髌骨且髌骨在trochlea的嵌入不足是最重要的一个因素。

(3)正确评估所有髌骨不稳定因素的影像学评估对于确定最佳治疗方案至关重要。

(4)在手术矫正中，必须考虑所有形态学、生物力学和功能性因素，以获得成功的治疗结果。