Correction of Patellar Height in Patellofemoral Instability

Abstract

The management of patellofemoral instability is based on a thorough evaluation of predisposing anatomical factors. Patella alta is one of the utmost causes of objective instability. The resulting biomechanical changes can lead to recurrent patellar instability, pain, and focal degenerative alterations. Physical examination is paramount in the decision-making process. Imaging evaluation has evolved from X-ray-based methods to magnetic resonance imaging measurements, which enable a more accurate assessment of the patellotrochlear relationship. Treatment is based on selective correction of the risk factors, while tibial tubercle distalization osteotomy as well as medial patellofemoral ligament reconstruction are tools that must be rationally considered. The present article reviews the surgical rationale for the treatment of patella alta in patellofemoral instability.

Keywords

patellar height - patellofemoral instability - tibial tubercle distalization osteotomy - tibial tubercle osteotomy - patella alta - distal realignment

Introduction

Patellofemoral instability presents predisposing anatomical and functional factors that trigger a clinical picture after an initial trauma of variable intensity. Following an acute episode of patellar luxation, symptoms recur in approximately one third of the cases.[1] The medial patellofemoral ligament (MPFL) is the most important static restrictor for patella stabilization, accounting for 50% to 60% of its containment to lateral displacement.[2] [3] Pathological studies have concluded that this injury occurs in up to 94% to 100% of acute dislocation cases.[4] [5] Therefore, MPFL reconstruction has been established as the standard stabilization technique for recurrent symptoms.

The current management of patellofemoral instability includes as well the treatment of predisposing factors; Evaluation of the other patellar stabilizers must be considered, as well as morphological evaluation of major and minor objective instability factors[6] (patellar height, lateralization of the tibial tubercle [TT], trochlear dysplasia, patellar tilt) and altered lower-limb alignment (genu valgus, genu recurvatum, and rotational changes).

Patella alta (also known as high-riding patella) is one of the most relevant anatomical factors in the decision-making process.[7] It is observed in 24% of objective patellofemoral instabilities,[6] defined as at least 1 true patella luxation and at least 1 anatomical abnormality. Due to its frequency, it is deemed a major instability factor and the only one that can result in a low-energy or atraumatic dislocation without some degree of trochlear dysplasia.[8] It is defined as a condition in which the patella is proximal to its normal position on the femoral trochlea.[9] It has no clear etiology. Some authors[10] consider it a congenital abnormality produced by the excessive length of the patellar tendon (> 52 mm), while others[6] describe it as a form of dysplasia and quadriceps shortening.

Biomechanics

Under normal circumstances, patellar engagement at the trochlear groove occurs during early knee flexion. The MPFL acts as a restrictor to the lateral patellar translation during the first 30° of flexion. Next, the main patellar stabilizer is the bone containment provided by the femoral trochlea.[11] If this does not occur as a result of an increased patellar height, the patella tends to lateralize due to the natural effect of the force vector generated by the quadriceps, perpetuating an instability as a result of increased mobility at the coronal plane of the patella.

Biomechanical studies[12] [13] [14] have shown that patella alta decreases the patellofemoral contact area, increasing contact stress, which in turn contributes to pain and focal osteoarthritis.

Under normal circumstances, the patellofemoral contact force increases along with knee flexion up to a point in which the quadriceps tendon contacts the trochlea for load distribution. This effect allows the tendon to support up to half the patellofemoral contact force during deep flexion (higher than 120°). In patella alta, load distribution towards the quadriceps tendon is delayed due to its higher position, resulting in a significant increase in the contact pressure of the patellofemoral cartilage.[14]

The normal patellofemoral contact area reaches a maximum point at 90° of flexion; next, it decreases progressively due to surface distribution from a wide central contact area to two smaller areas at the superolateral and superomedial regions of each facet, which are separated as the patella advances from the femoral trochlea toward the condyles at the intercondylar groove (≥ 120° of flexion).[11] Patella alta results in a reduced contact area from 0° to 60° of flexion, which is excessively increased on surfaces with no usual joint contact. As such, there is greater superficial deformation, leading to an increased contact area in intermediate and deep flexion ranges.[14] [15]

Clinical Evaluation

Clinically, the best way to assess patellar height is with the patient seated with the knees flexed at 90°. In subjects with normal anatomy, the patella is directed forward, while in those with patella alta, it faces the zenith in varying degrees.[16]

Patellar trajectory can be evaluated with the legs hanging over the table and extending the knees from a flexed position. The J sign is the abnormal lateralization movement of the patella during the final degrees of extension, indicating its movement away from the femoral trochlea. This is usually consistent with patella alta, trochlear dysplasia, or, more importantly, a combination of both.[17] [18] This clinical association has been confirmed by imaging studies. Ferlic et al.,[19] in a computed tomography-based study, found a direct correlation between patella alta and trochlear dysplasia. Zhang et al.[20] reported that subjects with a severe J sign (recurrent dislocation in extension) in the context of recurrent patellofemoral instability may present patella alta or rotational changes as independent anatomical risk factors when analyzed together with other major morphological factors.

The apprehension test (Smillie sign) assesses patellar stability at the trochlear groove. The patient is placed in supine position with extended knees and a relaxed quadriceps. From the contralateral side, the examiner places both thumbs on the medial edge of the patella, generating a lateral displacement while requesting an active knee flexion from the patient. Fearful or uncomfortable reactions to the test from 0° to 30° indicate an injury to the MPFL and associated medial supporting ligament structures.[21] [22] A positive test in flexion greater than 30° is highly suggestive of patella alta and other prevalent morphological changes, including trochlear dysplasia and TT lateralization.[22] More severe morphological changes are associated with greater knee flexion required for the apprenhension to cease. In patella alta, this is due to biomechanics, since the patella does not enter the trochlear groove at 30° flexion, meaning, there is no containment by the proximal portion of the lateral femoral condyle.[15]

Imaging Evaluation

From an imaging point of view, a true lateral projection of the knee flexed at 30° allows adequate tension of the patellar tendon for proper measurement of the patellar height.[23] A complete overlap of both femoral condyles corroborates a standardized view. Several validated methods have been described for the measurement of patellar height. However, their reliability depends on the variability of their anatomical landmarks.

The most widely used index for preoperative planning is the Caton-Deschamps (CD) index,[24] based on the distance from the patella to the tibial plateau, and not on tendon length, which is not altered by TT distalization.[25] In addition, it has high reproducibility compared to other indices,[26] [27] and is the only classical method to include a comparison with asymptomatic knees.[23] The CD index refers to the ratio between the distance from the lowest point of the patellar articular surface to the anterosuperior angle of the tibial plateau (B), divided by the length of the articular surface of the patella (A) ([Figure 1]). It is also known as the Lyon index,[28] since it was developed as a medical thesis by two students from the knee school from this city. It is widely used internationally due to its simplicity in determining the required distalization of the tubercle for normalization of the patellar height.

Fig. 1 Caton-Deschamps (CD) index. CD = B/A.

Patella alta is defined as a CD index higher than 1.2.[24] Other authors[9] [23] consider CD values higher than 1.3 abnormal, with no clear consensus. There are no gender-related differences, nor is the CD index significantly different with knee flexion between 0°-60°.[29] However, it is increased in subjects with immature skeleton due to incomplete ossification, which makes it difficult to assess the actual positioning of bone margins, generating false-positive results.[30] [31] The CD index changes significantly depending on whether an image is taken in supine position (with no quadriceps contraction) or standing up (with quadriceps contraction); most false-positive results are generated by the latter.[32] This explains why normal CD values must be adjusted according to quadriceps contraction:[29] 0.8 to 1.2 in supine position, and 1.0 to 1.4 while standing up. The measurements are also negatively affected by arthrosis.[23] [27]

Because of the variability in identifying the anterosuperior end of the tibia, particularly in arthritic knees with osteophytes, an angular measurement was validated for patients with patellar instability. This method is known as plateau-patella angle (PPA),[33] [34] has the advantage that its measurements are not altered by image magnification, patella size, or focal alterations of patellar enthesis. It has a good correlation with the CD index and high intra- and interobserver reliability.[33] The PPA is determined through lateral knee radiographs; it is formed by the intersection of a line tangential to the medial tibial plateau and a second line from the posterior end of the medial plateau to the lower end of the articular surface of the patella ([Figure 2]). Normal PPA values range from 21° to 29°. A PPA higher than 29° confirms patella alta.[33] [34] The PPA can be falsely modified by a significant alteration in tibial inclination at the sagittal plane.[34]

Fig. 2 Lateral radiograph of the knee in 30° of flexion for the determination of the plateau-patella angle (PPA).

Magnetic resonance imaging (MRI) for the determination of the CD index is associated with a series of considerations that do not allow its validation with the same criteria; in addition, it overestimates CD values, requiring an average addition of 0.18 point for comparison with the traditional radiographic method.[31] On the other hand, the Lyon Knee School and the French Arthroscopy Society[8] [35] highlight the importance of sagittal MRI to assess aspects other than patellar height and appreciate the real joint congruence between the patella and the distal femur, considering the significant differences existing in the articular geometry of the cartilage and the corresponding subchondral bone anatomy of the patella and trochlea. The sagittal patellofemoral engagement index was defined[35] based on Biedert and Albrecht's initial MRI study.[36] It enables the assessment of whether a radiographic patella alta has an indication for patellar distalization based on the correlation that must be observed when the cartilage of the trochlea and the patella are superimposed at the sagittal plane. It is the quotient between the image showing the greatest length of the patellar cartilage superimposed to one in which the trochlea cartilage is at its most proximal point. The measurement is based on the length in contact with the patellar cartilage ([Figure 3]). Its normal value is higher than 0.45 (engagement greater than 45%) with the knee in extension, and no quadriceps contraction or weight bearing. This would support the theory that the relationship between trochlear and patellar cartilages would have more clinical and imaging relevance than the bony landmarks from the patella and the tibia.[37] [38]

Fig. 3 Sagittal engagement index = TL/PL. The normal value is higher than 0.45. The image shows patella alta with adequate chondral engagement at the trochlear groove, with no indication for patellar distalization. PL: patellar length, TL: trochlear length.

Indications

Due to the multifactorial nature of the risk assessment in patellofemoral instability, there is no optimal, universally accepted treatment algorithm.[39] The management is based on a selective correction of causal factors, with the internationally expanded concept of à la carte surgery developed by the Lyon school.[28] [40]

The authors of the present study believe, supported by the literature,[18] [41] [42] that MPFL reconstruction is essential in all patients with patellofemoral instability regardless of underlying abnormalities. As such, two goals are achieved: to restore the function of the main stabilizer of the patella, which is injured after an episode of patellar dislocation in more than 90% of the cases,[4] [5] and to abolish the apprehension in the initial ranges of knee flexion. A systematic review[43] showed that the lack of this surgical procedure results in persistent clinical signs despite bone realignment in up to a third of the cases. However, the isolated reconstruction of the MPFL is insufficient if the morphological factors are not considered with caution. Magnussen[18] states that a Smillie sign relieved in 30° to 40° of flexion suggests good outcomes from the MPFL reconstruction alone, while a persistent apprehension at 45° to 60° of flexion reflects a significant morphological change that should be corrected by distal realignment (TT osteotomy).

A systematic review by Tompkins and Arednt[39] detailed that reports of high success rates with MPFL reconstruction alone actually excluded high morphological risk conditions (high-grade trochlear dysplasia, patella alta, and abnormal TT lateralization) on two thirds of the studies. Recently, a group from Lyon carried out a study[44] with 211 cases treated with MPFL reconstruction alone, and followed up for a minimum period of 3 years. These authors[44] evaluated clinical outcomes and failure predictors based on preoperative clinical and radiological variables (including the measurement of all major instability factors), and found out a significant relationship of poor outcomes with positive J sign and patella alta with CD indices ≥ 1.3.[44] In addition, another group[45] evaluated the influence of MPFL reconstruction alone on patellar height, concluding that distalization osteotomies must not be indicated for patients with patellar instability and CD indices from 1.2 to 1.4 because MPFL reconstruction causes a mean patellar distalization of 0.2. Furthermore, these authors[45] found that correction of patella alta with CD index higher than 1.4 is only achieved in 50% of the cases.

Combined MPFL reconstruction and TT osteotomy is a safe, effective procedure.[46] However, there is no consensus on a limit value for patellar height to determine when TT distalization is indeed required.[9] [47] The authors of the present study believe, based on the available evidence,[17] [18] [20] [21] [22] [35] [42] [44] [45] [48] [49] that the decision for tubercle distalization must be based on three aspects: physical examination (impaired J sign and results of the apprehension test), radiographic study (CD index higher than 1.4), and MRI (altered sagittal patellofemoral engagement index) ([Figure 4]).

Fig. 4 Indications for tibial tubercle (TT) osteotomy. The clinical and imaging evaluations are essential for adequate decision-making due to the lack of consensus to indicate distalization in patella alta. CD index: Caton-Deschamps index.

Another approach to consider in the treatment of patellofemoral instability is the direct relationship between patella alta and trochlear dysplasia.[19] Patella alta contributes to instability due to the delayed entry of the patella into the trochlea during knee flexion, resulting in lateral displacement.[15] Similarly, trochlear dysplasia with groove flattening leads to lower patellar constriction, particularly in its most proximal portion, which is common in low-grade dysplasia (Dejour type A). A more distal crossover sign on a lateral knee radiograph indicates a more severe trochlear dysplasia.[50] Since both morphological changes decrease patellar stability by similar mechanisms, tibial tubercle distalization can be considered even at a borderline patellar height (CD index ranging from 1.2 to 1.4) to optimize its femoral engagement.[18] On the other hand, a recent review article by Rush and Diduch[17] pointed out that, in high-grade dysplasia (Dejour type B and D), the effect of the supratrochlear spur can be minimized by TT distalization, leaving the bump effect proximal to the patellochlear engagement; this cancels the ski ramp, which accounts for patellar lateralization in early flexion. This is especially relevant in borderline trochlear dysplasia with significant patella alta (CD index higher than 1.4) and a spur up to 5 mm, obviating the need for trochleoplasty.

Surgical Technique

The preferred surgical procedure for the treatment of patella alta ([Figure 5A]) is the anterior tibial tubercle distalization osteotomy ([Figure 5B]).[43] In this surgery, the patellar tendon attachment is transferred distally, enabling patella repositioning at an appropriate height regarding the trochlea and improving patellofemoral stability ([Figure 5C]). Neyret et al.[10] have proposed a modification to the traditional technique, adding a patellar tendon tenodesis to restore its normal length and provide greater coronal stability ([Figure 5D]). This is achieved with two anchors at the original TT position, 3 cm from the joint line.[10] [51]

Fig. 5 (A) Patella alta. (B) Tibial tubercle (TT) osteotomy. (C) Traditional osteosynthesis technique. (D) Modified technique with patellar tenodesis.

Clinical studies[43] [51] have shown that both procedures ([Figures 5C] and [5D]) decrease patellar height, reduce the probability of patellofemoral dislocation, and improve the outcomes in patient-reported satisfaction surveys. A recent biomechanical study[52] evaluated patellofemoral contact after both procedures under controlled conditions of distal transfer. This study[52] found out that osteotomy alone generates less stress on the cartilage, in addition to requiring a shorter displacement distance to achieve its goal.

As a general aspect of the technique, a longitudinal incision of 5 cm to 6 cm is made along the medial margin of the tibial tubercle for complete TT exposure. This approach also enables the harvest of a semitendinosus or gracilis autograft for MPFL reconstruction, which is usually performed at the same surgical time, after the osteotomy.[16] [49]

The proximal limit of the osteotomy is located at the patellar tendon attachment. With an oscillating saw or osteotome, a bone block of at least 6 cm in length is obtained, which this length can be increased depending on the amount of distal displacement planned. Three section types can be used to obtain the osteotomized fragment: a stepped section (perpendicular to the section axis), a beveled section, and a section parallel to the anterior cortex. Each configuration has associated variants that must be recognized to avoid complications ([Figure 6]).

Fig. 6. Configuration of a tibial tubercle (TT) osteotomy. (A) Osteotomy parallel to the tibial anterior cortex. Note the risk of extending the osteotomy to the tibial plateau. (B) Osteotomy with beveled proximal inclination. Posterior to the patellar tendon (recommended). (C) Osteotomy with stepped proximal inclination, which can affect the distal patellar tendon attachment, risking an iatrogenic rupture. (D) Osteotomy parallel to the anterior edge of the TT. Note that it affects the total thickness of the anterior cortex of the tibia, increasing the risk of fracture. (E) Anterior oblique osteotomy. There is risk of fracture and non-union due to excessive cortical thinning and iatrogenic rupture of the patellar tendon.

The degree of distal osteotomy displacement is calculated by subtracting the lengths that make up the CD index, with the goal of achieving a value equal to 1.0 at the postoperative period.[25] [53] The correction must not exceed 15 mm to avoid excessive tension of the extensor mechanism and flexion limitation resulting from an iatrogenic patella infera.[8]

The osteotomy must be deep enough to enable the incorporation of a sufficient amount of cancellous bone (> 8 mm) to reduce the risk of nonunion.[51] To avoid difficulties in drilling the insertion holes to fixate the screws, it is suggested that the first cortex of each screw must be opened prior to osteotomy. Using a small oscillating saw, two distal transverse sections (parallel to each other) are made in the osteotomy block to achieve osteotomy stability after tubercle mobilization.

After the distal transfer, the osteotomy is fixed with two 4.5-mm full-thread cancellous screws, which must pass through the second cortex under radiological confirmation to achieve adequate compression and avoid complications during consolidation. Each screw is separated by 2 cm, and the most proximal screw must be 2 cm away from the proximal margin of the osteotomy ([Figure 7]). It is suggested to initially fix the distal screw (not completely adjusted) to enable TT medialization if required.[8] Finally, the distal end of the osteotomy is checked to adjust the bone block at the required level and in apposition with the surrounding tibia ([Figure 8]).

Fig. 7 Osteotomy to decrease the patellar height. Ideally, the osteotomized bone block must be 6 cm long, fixed with two 4.5-millimeter screws, 2 centimeters apart from each other and their bone ends.

Fig. 8 Surgical planning for tibial tubercle (TT) osteotomy. (1) Calculation of the patellar height. CD: Caton-Deschamps index. (A) Length of the articular surface of the patella. (B) Distance between the distal articular end of the patella and the anterosuperior angle of the tibial plateau. (2) Calculation of tubercle distalization. DR: osteotomy for distal resection. (3) Corrected measurement of the patellar height. According to the distalization planned, the postprocedural patellar height can be calculated using the formula described. (4) Size of the osteotomy. According to the formula. X: Length of the osteotomy. (5) Delimitation of the osteotomy. According to X. (6) Delimitation of the distal resection. Two transverse sections, parallel to each other, are made according to the size of the DR. (7) Postprocedural final patellar height.

Servien et al.[54] published the radiological results from a group of 38 patients who underwent TT transfer (distalization and/or medialization). They observed a medializing effect in the cohort of 12 patients submitted to distalization osteotomy alone, with a reduced tibial tubercle-trochlear groove (TT-TG) distance ranging from 3 mm to 4 mm (with no statistical significance). This effect has been cited in several subsequent publications.[8] [49] [55] However, as of the date of this review, we have not found any studies confirming its reproducibility, warranting further research. Taking these results into consideration, Weber et al.[42] recommended tibial tubercle distalization in cases with combined morphological factors of patellofemoral instability and a TT-TG distance higher than 15 mm. This theoretically enables the management of the patellar height and normalization of the TT-TG distance with no need for medialization. In contrast, our group have reported recently[56] that the patellar height decreases significantly (reaching normal values) following an MPFL reconstruction combined to an Emslie-Trillat medialization osteotomy. This is greater in cases with severe patella alta (CD index > 1.4), constituting a new alternative for patellar height correction in patellar instability.[56]

Currently, the number and orientation of fixation screws for osteotomy can be recommended based on biomechanical evidence. Warner et al.[59] evaluated the stiffness of two 4.5-mm screws and three 3.5-mm screws and concluded that both devices are comparable, with the advantage that small fragment screws are less associated with the need for subsequent removal due to prominence and soft-tissue irritation. Regarding screw configuration, Chang et al.,[60] using a finite element analysis, demonstrated that the parallel horizontal and distal oblique orientations provide the greatest bone-fragment stability under cyclic loads ([Figure 9]).

Fig. 9 Small fragment screws (3.5 mm) for the fixation of the tibial tubercle (TT) distalization osteotomy. (A) The screws must be arranged equidistant from each other and from the ends of the osteotomized bone fragment. (B) The screws must be placed in a horizontal parallel (as shown) or lower oblique orientation, since these are the most biomechanically stable configurations.

Complications

The complication rate does not exceed 7%. The most frequent complication is symptomatic osteosynthesis material.[48] To a lesser extent, Surgical site infections (1.2%) and deep vein thrombosis (0.6%) have been reported.[43]

Proximal tibial fractures are uncommon (1% to 2.6%); most of them are resolved conservatively by immobilization for 6 to 8 weeks.[48] Their origin does not seem to be influenced by screw size,[61] but by the change of limb stance phase from partial to full load.[62]

Popliteal artery injury is rare, but potentially devastating. Bernhoff and Björck[63] have reported an incidence of popliteal artery injury of 0.11% in a group of 1,831 TT osteotomies. To determine artery location at this level, Hernigou et al.[64] identified landmarks to minimize risk and define a safety zone for the placement of bicortical screws. On average, the distance between the artery and the posterior tibial cortex was of 12 mm. The minimum distance between these structures increases from the proximal to the distal third of the TT. The safety zone for the placement of bicortical screws is at the posteromedial region of the proximal tibia and the posterocentral medial third, 2 cm distal to the most prominent TT region and oriented perpendicular to the tibial crest.

Other complications include osteotomy malunion (delayed union or nonunion), arthrofibrosis, and deep peroneal nerve injury.[65]

Postoperative Care

After the procedure, the patient must use a knee immobilizer orthosis graduated from 0° to 30° for active joint range and loading exercises for 3 weeks.[53] Passive joint range exercises are allowed from the first day, limited to 100° of flexion during the first month to avoid excessive stress at the osteotomy fixation.[53] At the sixth week, the immobilization is removed, and closed kinetic chain exercises between 0° to 60° are added to strengthen the muscles. Active mobilization in full joint range is allowed. Weight load increases progressively from the third to the eighth weeks, when full load is allowed.[49] Bicycle exercises are allowed from the second month on, and swimming, from the third month on. Sports activities can be resumed after six months.[53]

Results

Distal realignment osteotomy is effective for the normalizing of patellar height. The rates of postprocedural recurrent dislocation range from 0% to 4.9%, with an average risk of 1.75%.[43] Subjective instability is significantly higher than the risk of objective dislocation. In a systematic review,[43] the apprehension sign was positive in 15% to 33% of patients, with an average risk of 26.3%. However, these data must be evaluated with care because most studies included in this review did not perform MPFL reconstruction. There are no studies that enable a comparison of patient-reported pre- and postoperative assessment scores.

Conclusions

The management of patellofemoral instability is based on an adequate evaluation of predisposing anatomical alterations. Patella alta is one of the most important causes of objective instability. It causes a biomechanical alteration which can potentially lead to recurrent patellar luxation, pain, and focal degenerative changes. The physical examination is essential to the decision-making process. Imaging techniques have evolved from radiography-based methods to MRI measurements, which enable a more complete orientation of the relationship between the patella and the femoral trochlea. The treatment is based on the selective correction of causal factors, and TT distalization osteotomy and MPFL reconstruction are techniques that must be considered rationally. A series of recommendations to summarize these principles are presented in [Table 1].

Table 1

	Final recommendations
1	X-ray: use the Caton-Deschamps (CD) index. Patella alta: CD > 1.2 in supine position. CD > 1.4 while standing up (with quadriceps contraction).
2	Magnetic resonance imaging: use the patellofemoral engagement index. Patella alta: engagement < 0.45 (45%).
3	Calculation of the distal bone resection: target: CD index = 1. Patellar height: CD = B/A. Distal resection (DR) = B – A. Corrected height: CD = B – DR/A.
4	Limit of the distal bone resection: 15 mm.
5	Anteromedial approach: it facilitates hamstring harvesting if associated with reconstruction of the medial patellofemoral ligament.
6	Length of the tibial anterior tubercle osteotomy: ≥6 cm, depending on the distal resection block. Goal: to leave 5 cm to 6 cm of bone fragment to reduce the risk of nonunion.
7	Limit of the proximal osteotomy: above the patellar tendon enthesis.
8	Thickness of the osteotomy: minimum: 8 mm. Maximum: 10 mm. Ensure cancellous bone inclusion to stimulate adequate bone consolidation. The thickness of the osteotomy must be lower than the full thickness of the patellar tendon.
9	Shape of the osteotomy: beveled proximal or distal inclination (most commonly recommended).
10	Osteosynthesis: at least two 4.5-mm screws or three 3.5-mm screws equidistant from each other. Screw orientation: horizontal parallel or distal oblique.
11	Drill the first cortex before completing the osteotomy: this avoids difficulties in creating equidistant holes in a stable, motionless bone. Remember to delineate the distal resection.
12	After completing osteotomy + distalization: complete the drill in a posterocentral or posteromedial direction to reduce the risk of vascular injury. Use fluoroscopy and new drills to have more control over the cortical perforation.
13	Fixation: start with the most distal hole to medialize the osteotomy if required.

Conflicto de Intereses

Los autores declaran no tener ningún conflicto de intereses.

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Publication History

Received: 28 September 2019

Accepted: 16 November 2020

Article published online:
02 June 2021