The effects of patellar tendon advancement on the immature proximal tibia

Abstract

Purpose

The aim of this study is to examine the short-term effects of patellar tendon advancement on the proximal tibial slope in the skeletally immature patient.

Methods

A retrospective, non-randomized, comparative cohort design was used. Koshino indices and tibial slopes were assessed pre-operatively and post-operatively and compared with age- and sex-matched controls.

Results

Nine children with 17 patellar tendon advancements were analyzed for changes in Koshino indices. Of these 17 tibiae, radiographs on changes in tibial slope were available for 16 tibiae which were also compared with controls. Children aged <11 years had a greater initial posterior tibial slope (69.8° ± 3.5°) than age-matched controls (80.3° ± 2.7°). A decrease in posterior slope was seen in these younger patients (average change 10.3° ± 4.8°) at an average of 1.6 years of follow-up. Of the nine apophyses in children aged <11 years of age, seven had undergone premature closure.

Conclusion

Patellar tendon advancement appears to have an unreported effect on the proximal tibial growth in the young patient (<11 years old). These patients appear to be susceptible to apophyseal closure, resulting in subsequent loss of posterior tibial slope. Surgeons should be aware of this effect and monitor younger patients with radiographs if performing this procedure.

Introduction

The normal proximal tibia has a posterior slope from 7° to 15° in the adult knee [1–3]. In their study on 76 children with knee abnormalities, Gugenheim et al. [4] found that when knee flexion contracture is present, the posterior slope of the tibia was significantly greater in these children than the normal population. This increase in posterior slope may be the result of increased tension on the anterior aspect of the tibial tubercle, leading to increased growth. It may also be speculated that the more posteriorly located weight-bearing axis in patients with flexion contractures can add to the increased posterior slope of the tibia by adding a compressive load to the posterior growth plate. This would result in growth retardation manner similar to that seen in other pathologic states, such as Blount’s disease, where excessive mechanical loading results in varus angular deformities about the knee [5, 6].

Crouch gait is a common and often progressive form of gait impairment seen in cerebral palsy and manifests as fixed hip and knee flexion and associated fixed ankle plantar flexion or excessive dorsiflexion. The pathogenesis of crouch gait is usually related to the combined factors of weakness, spasticity, contracture, quadriceps insufficiency, and bony rotational malalignment. As Gage [7] pointed out, crouch gait may be due, at least in part, to iatrogenic factors, such as over-lengthening of the triceps surae. These authors also note that this pathological gait pattern encompasses a “continuum” from mild to severe. In general, crouch gait refers to knee flexion of >20° at initial contact and mid stance, with excessive ankle dorsiflexion, as well as continuous knee extensor moment during stance. In the more severe forms of crouch gait, rebalancing of the overstretched knee extensor mechanism is required to achieve an upright stance.

Single-event multilevel surgery is now becoming the normal method of treatment for these patients. One procedure that may be included in multilevel surgery prior to skeletal maturity in children with a crouched gait is patellar tendon advancement. Often this procedure is combined with distal femoral extension osteotomies to treat severe crouched gait in children with cerebral palsy [8]. Gage [7] found retensioning of the quadriceps mechanism to be important in improving the gait and knee kinematics in such children. Novacheck et al. [9] concluded that patellar tendon advancement was essential to achieve optimal results in multilevel surgery for the correction of persistent crouch gait. More recently, Das et al. [10] have shown improvements in function and quadriceps strength with decreases in knee pain following similar multilevel procedures. To prevent damage to the apophysis and therefore to the proximal tibial growth plate, the patellar tendon is carefully removed from the apophysis and inserted at a more distal level into the periosteum of the tibia. Gage reported an improvement in knee kinematics between patients undergoing extension osteotomy of the distal femur combined with patellar tendon advancement over the osteotomy alone [7]. Stout et al. [8] found that the inclusion of bony patellar tendon advancement was necessary for optimal results when evaluating patients with crouch gait following distal femoral extension osteotomy with or without patellar tendon advancement for quadriceps insufficiency. Stout et al. [8] demonstrated improved kinematics and quadriceps strength with patellar tendon advancement only. Despite its increasing use and apparent beneficial effects on gait, the effects of patellar tendon advancement on the skeletally immature tibia is unknown.

The aim of this study was to examine the effect of patellar tendon advancement on the growing proximal tibia. We hypothesize that (1) patellar tendon advancement in the skeletally immature patient would lead to decreased patella alta, as measured by a decrease in the Koshino index (KI), (2) this procedure would cause a decrease in the posterior slope of the proximal tibia, and (3) this decrease would be greater in younger children.

Materials and methods

The participating institution’s Institutional Review Board approved this study. A retrospective, non-randomized, comparative cohort design was used. Consecutive patients who had initial treatment from January 2003 to November 2008 were identified by Current Procedural Terminology (CPT) codes. Inclusion criteria were (1) diagnosis of cerebral palsy and crouch gait by clinical evaluation or gait analysis and (2) history of patellar tendon advancement with open physes. The diagnosis of crouch gait was determined using either clinical evidence of clinically relevant hip and knee flexion contracture on physical exam or a >20° of knee flexion at initial contact and mid stance, with excessive ankle dorsiflexion under gait laboratory motion analysis [11]. One patient in the study met the clinical inclusion criteria for crouch gait but did not demonstrate similar criteria in the motion laboratory analysis. Exclusion criteria were bony advancement of the patellar tendon or follow-up of <1 year. For the purpose of the analysis, patients were stratified by age into two groups: those <11 years of age (patients receiving surgery up until their eleventh birthday) and those ≥11 years of age (patients receiving surgery on the day of their eleventh birthday or after).

Surgical technique

Two surgeons utilizing a technique similar to that detailed by Novacheck et al. [9] performed all patellar tendon advancements in this study. A direct anterior midline incision was made from the inferior third of the patella to just distal of the tibial apophysis. The subcutaneous tissue was sharply dissected down to the patellar tendon sheath, which was separated from the underlying patellar tendon. The medial and lateral borders of the patellar tendon were identified. The tendon was sharply released from the cartilage apophysis leaving about 2 mm of fibrous tendon to avoid injury to the cartilaginous growth plate. The tendon was then released fully, and Krackow stitches were placed at the end of the tendon. After the distal extent of the tibial apophysis was verified with fluoroscopy, the periosteum was marked, and a t-shaped incision was made in the anterior tibial periosteum. The medial and lateral portions of the periosteum were then elevated, creating a window where the patellar tendon could be placed with advancement. A transverse drill hole was placed just proximal to the mid patella from medial to lateral. A second drill hole was placed transversely from medial to lateral in the tibial diaphysis posterior to the periosteal window already developed. A wire was then passed through the patella down through the tibia and tightened to a point that the anterior pole of the patella was between the Blumensaat line and the tibial plateau—but no further distally. The patellar tendon was then sutured directly to bone suturing the periosteal flaps over and into the substance of the patellar tendon. The wound was irrigated and closed using a standard technique.

Early in the study when stainless steel wires were used, they typically broke after 1 year and were removed if symptomatic. After a significant portion of the patients showed evidence of broken wires and underwent hardware removal for symptomatic hardware failure, we changed our protocol to the use of woven cerclage cable 1.3 mm in diameter; this cable was used in the same tension band fashion as the wires for post-operative mechanical protection of our tendon advancement. In the manner similar to that used for the wires, the 1.3-mm-diameter cerclage cable was advanced utilizing the same drill holes and placed in a tension band fashion. A standard cable swage was then used to set the length of the tension band construct. This change in protocol prevented hardware failure, but it became standard practice to remove symptomatic cables at 12 months post-operatively, thereby limiting our ability to assess the mechanics of the protocol change.

Radiographic evaluation

Patient charts were reviewed to obtain the age of each patient at the time of the procedure and the types of procedures performed during surgery. Pre-operative and post-operative radiographs were reviewed using a digital radiograph picture archiving and communication system (PACS) and its software package. The KI of each of the involved extremities was calculated on the available pre-operative and post-operative lateral radiographs using the method of Koshino and Sugimoto [12]. In this method, a line is drawn from the epiphyseal line of the distal femur and proximal tibia. A longitudinal line is then drawn along the length of the patella at the midportion. The KI is then calculated by taking the ratio of the distance of a line drawn from the midportion of the length of the patella to the midportion of the proximal tibial epiphysis over the distance of a line drawn from the midportion of the distal femoral epiphyseal line to the midportion of the proximal tibial epiphyseal line (Fig. 1). This method has been shown to be a reliable and accurate method of evaluating patella alta in the adolescent population [12]. The degree of correction achieved during the distal femur extension osteotomy was calculated utilizing pre-operative and post-operative lateral radiographs. The posterior distal femur cortex was used to calculate the degree of extension achieved during the osteotomy and fixation.

Fig. 1 The Koshino index (KI) is calculated using a lateral radiograph of the knee. The midportions of a line along the length of the patella, the distal femur epiphysis, and the proximal tibial epiphysis, respectively, are utilized. The KI is then calculated as the ratio of the distance of a line drawn from the midportion of the patellar line to the midportion of the proximal (P) tibial epiphyseal line (PT) over the length of a line from the midportion of the distal femur (F) epiphyseal line to the midportion of the proximal tibia epiphyseal line (FT) The KI is calculated as KI = PT/FT and is a ratio with no unit of measurement. A range of 0.99–1.20 is considered to be normal, and the KI tends to be stable throughout a knee range of flexion from 30° to 90°

The tibial slope of each involved extremity was recorded as the angle between the anterior cortex of the tibial shaft and the posterior aspect of a transverse line approximating the epiphysis of the proximal tibia. One reviewer measured the tibial slope of all involved extremities three times, and the average of these values was used for the analysis of both the pre-operative and post-operative lateral radiographs. When a pre-operative radiograph was not available for review, the first post-operative radiograph taken during the initial procedure hospital stay was used for slope evaluation. The most recent post-operative radiograph was examined to evaluate for premature apophyseal closure, as defined by the closure of proximal tibial apophysis prior to closure of the proximal tibial growth plate. Age- and sex-matched controls were obtained using the participating institution’s PACS system, and each of these control patients was evaluated for both pre-operative and post-operative comparisons. Two controls were utilized for each patient, one for the pre-operative comparison and one for the post-operative comparison. The same reviewer recorded the tibial slope for the matched control for both the pre-operative and post-operative controls for each patient in the study. The same method of measuring the matched controls three times was utilized, and the average of the values was used for comparison to the patients involved in the study.

Microsoft Excel (Microsoft, Redwood, WA) was used to perform the statistical analysis. The two-tailed Student t test was used to determine if there was a significant difference in the Koshino indices of patients before and after patellar tendon advancement with or without concomitant distal femoral extension osteotomy. The two-sided Student t test was also used to determine if there was a significant difference in the posterior tibial slope pre-operatively and post-operatively of the patients <11 years of age versus those ≥11 years old at the time of surgery, and between subjects and age- and sex-matched controls for those <11 years of age and those ≥11 years of age. Significance was determined at p < 0.05 for all statistical analyses.

Results

Nine patients with 17 patellar tendon advancements met the inclusion criteria at the time of review. There were adequate radiographs of 16 tibiae to allow for posterior slope measurements. All patients had a diagnosis of diplegic cerebral palsy, one patient was Gross Motor Function Classification System (GMFCS) I, while the other eight patients were GMFCS III. The average follow-up time in the study was 19.2 months, the average follow-up time of patients aged <11 years was 19.2 (±4.8) months, and average follow-up time of patients aged ≥11 years was 19.2 months (±1.2 years). The average age of the nine patients at time of surgery was 11.8 (range 9.2–14.3) years; five patients were <11 years and four patients were aged ≥11 years. Of the patients aged <11 years at time of surgery, two were male and three were female; of the patients aged ≥11 years, all were male. The average age at time of surgery of patients aged <11 years and ≥ 11 years was 123.8 (range 110.2–131) and 158.4 (range 143.2–172.2) months, respectively. The pre-operative physical findings and status of gait analysis are presented in Table 1. All additional procedures performed on these children are listed in Table 2 along with the degree of correction achieved with the distal femur extension osteotomy. Eight of nine children who had patellar tendon advancement also had a distal femur extension osteotomy performed with the use of locking plate fixation of the distal femur osteotomy.

Table 1 Patient pre-operative examination

Patient	Pre-operative gait analysis?a	Right pre-operative FFD (°)	Left pre-operative FFD (°)	Right pre-operative PA (°)	Left pre-operative PA (°)
1	Yes	35	35	145	145
2	Yes	0	0	140	140
3	Yes	20	20	145	140
4	Yes	15	20	NA	NA
5	Yes	15	15	130	130
6	Yes	30	25	125	125
7	No	30	30	135–140	135–140
8	Yes	NA	NA	35	50
9	No	30	30	125	130

The pre-operative fixed flexion deformity (FFD) and popliteal angles (PA) determined from chart review are listed here when available

^aThe status of whether pre-operative motion analysis was performed

Table 1 Patient pre-operative examination

Table 2 Surgery details

Patient	Left distal femur correction (°)	Right distal femur correction (°)	Associated procedures
1	44	27	Right: DFO, AT, TO Left: DFO
2	0	0	Bilateral: VO
3	24	34	Bilateral: DFO, PL, HL
4	22	14	Bilateral: DFO
5	−9	6	Bilateral: FDRO, PL, HL Left: TO
6	21	24	Bilateral:DFO, HL
7	29	19	Bilateral:DFO Right: TAL, PT
8	24	0	Bilateral: AT, HL, TO, GR Left: DFO
9	33	25	Bilateral: DFO, PL, HL

The degree of distal femur extension correction achieved intra-operatively as well as the additional procedures performed during the index procedures are listed

DFO distal femur extension osteotomy, AT adductor tenotomy, TO supramalleolar tibial osteotomy, VO varus derotational osteotomy, PL psoas lengthening, HL hamstring lengthening, FDRO femoral derotational osteotomy, TAL tendoachilles lengthening, PT posterior tibial tendon release, GR gastrocnemius recession

Table 2 Surgery details

The pre-operative and post-operative Koshino indices (KI) were recorded and stratified by age (Table 3). Overall, there was a statistically significant decrease in the KI of patients following surgery. The younger patients did have a lower average pre-operative KI when compared with the older children; however, there was no statistically significant difference in KI improvement noted when the patients were stratified by age. While slight differences in pre-operative KI were observed [1.15 ± 0.16 (<11 years old) vs. 1.28 ± 0.06 (≥11 years old); p = 0.03], both cohorts experienced a significant change in these measurements post-operatively (0.94 ± 0.11 and 0.99 ± 0.10; p < 0.01). There were no significant differences between the post-operative KI of the two cohorts (0.94 ± 0.1 vs. 0.99 ± 0.1, respectively; p = 0.3) or in the change in KI (0.21 ± 0.18 vs. 0.26 ± 0.10, respectively; p = 0.59).

Table 3 Koshino index results

Patient cohort	Pre-operative KI (°)	Post-operative KI (°)	Change in KI
Overall			p < 0.0001
	1.21 (0.13)	0.97 (0.10)	−0.23 (0.16)
Age (years)	p = 0.03	p = 0.3	p = 0.59
<11	1.15 (0.16)	0.94 (0.11)	−0.21 (0.18)
≥11	1.28 (0.06)	0.99 (0.10)	−0.26 (0.10)

The standard deviation (SD) is given in parenthesis

The Koshino Indices (KI) for all patients (Overall) and for patients stratified by age grouping are listed. Overall, there was a decrease in the KI of 0.23, giving a relative correction of patella alta (p < 0.0001). For the pre-operative evaluation of patella alta, there was a statistically significant difference in the KI for patients aged <11 years versus those aged ≥11 years (p = 0.03)

Table 3 Koshino index results

The results of the posterior tibial slope analysis are shown in Tables 4 and 5. The pre-operative slopes were compared to the post-operative slopes for all of the patients (Overall) and according to age group. All but one tibia showed a loss of posterior tibial slope; no change was seen in this single tibia. We observed a significantly greater initial posterior tibial slope in our patients aged <11 years (69.8° ± 3.5°) than in those aged ≥11 years (76.5° ± 6.3°) (p = 0.03) and the age-matched controls (80.3° ± 2.7°) (p < 0.001). Additionally, following patellar tendon advancement, a significantly greater change in the tibial slope (loss of slope) was observed in those aged <11 years (10.3° ± 4.8°) than in those aged ≥11 years (2.8° ± 2.5°) (p = 0.002). This change in the posterior slope of the younger patients (80.1° ± 4.3°) resulted in tibial slope values that were similar to those of the age-matched controls (76.4° ± 3.3°) (p = 0.06) and to the initial slope values in the older patients (76.5 ± 6.3) (p = 0.2). One patient had a significant slope reversal from 70.3° pre-operatively to 88.7° post-operatively and actually went on to require further surgical correction of the posterior tibial slope (Fig. 2).

Table 4 Results of the posterior tibial slope analysis

Patient cohort	Pre-operative value (°)	Post-operative value (°)	Change (°)
Overall	73.4 (6.2)	79.0 (5.3)	5.7 (5.3)
Stratified according to age group	p = 0.03	p = 0.78	p = 0.002
<11	69.8 (3.5)*	80.1 (4.3)*	10.3 (4.8)
≥11	76.5 (6.3)**	79.3 (6.3)**	2.8 (2.5)
Average follow-up
<11 years of age	1.6 years	*p = 0.0002
≥11 years of age	1.6 years	**p = 0.03

The SD is given in parenthesis

The overall tibial slope values pre- and post-operative are listed, as well as change in tibial slope stratified by age group. Pre-operatively there was a statistically significant difference in the posterior tibial slope for patients who were aged <11 years compared to those aged ≥11 years (p = 0.03). Post-operatively, the change in tibial slope was statistically significantly different between patients aged <11 years and those aged ≥11 years. Within each age grouping, the pre-operative tibial slope was statistically significantly different from the post-operative values in both groups of patients [<11 years (p = 0.0002) vs. ≥11 years (p = 0.03)]. The average time to follow-up of patients aged <11 and ≥11 were similar

*, ** Significant atp < 0.05 and 0.001, respectively

Table 4 Results of the posterior tibial slope analysis

Table 5 Results of the posterior tibial slope analysis versus matched controls

Study cohort	Pre-operative values (°)	Post-operative values (°)
Age of <11 years	p < 0.0001	p = 0.06
Subjects	69.8 (3.5)	80.1 (4.7)
Controls	80.3 (2.7)	76.4 (3.3)
Age of ≥11 years	p = 0.63	p = 0.8
Subjects	76.5 (6.3)	79.3 (6.3)
Controls	77.8 (2.0)	78.6 (4.3)

The SD is given in parenthesis

The tibial slope for subjects and for age-matched controls is compared. Pre-operatively, the tibial slope of patients aged <11 years was statistically significantly different from that of the age-matched controls (p < 0.0001). Although it did not reach statistical significance, there was a trend towards a more anteriorly angled tibial slope post-operatively in younger patients compared to age-matched controls (p = 0.059)

Table 5 Results of the posterior tibial slope analysis versus matched controls

Fig. 2 Example of a patient who experienced a closed apophysis following patellar tendon advancement resulting in an increased anterior tibial slope requiring a revision osteotomy

A review of the initial and most recent radiographs to evaluate for premature closure of the tibia tubercle (defined as apophyseal closure on radiographs prior to tibial physeal closure) demonstrated that seven of the nine physes in the younger age group and six of the seven physes in the older group showed premature closure of the apophysis. The average time to premature closure of the apophysis in the younger and older age groups was 19 (range 15.5–21.5) and 19 (range 17.2–20.7) months, respectively.

Discussion

Patellar tendon advancement has been shown to be an effective treatment for patients with crouch gait [7–10]. This procedure is performed using a tension band cerclage to provide mechanical stability to the advanced patellar tendon while it heals. The KI presented here indicate that patellar tendon advancement is associated with an improvement of patella alta, which is similar to the results found by Stout et al. [8]. The KI was lowered following patellar tendon advancement, with no significant difference in the change according to ages of the patients (<11 and ≥11 years).

The results of our study are the first to demonstrate the effects of patellar tendon advancement on the growing tibia. Younger patients (<11 years) appear to be more susceptible to the effects on the tibial slope than patients aged ≥11 years. The premature closure of the anteriorly located apophysis is the most likely cause of the change in posterior slope. Various mechanisms may lead to this premature closure, and they may be acting independently or in concert to give the final result. One possible mechanism is occult injury to the anterior growth plate during surgery, resulting in the anterior tethering observed in this study. All patients may be susceptible to this type of injury (7/9 premature apophysis closure in the younger group and 6/7 in the older group), but it appears that the younger patients, who have a relatively greater growth potential, are more at risk for the changes in their tibial slope observed on radiographs, likely due to the remaining growth.

Other contributing etiologies may be the change in the tensile/compressive force across the apophysis and anterior growth plate. As the patellar tendon is moved from proximal to distal across the growth plate, the forces crossing the growth plate could switch from tensile to compressive in the anterior growth plate, inhibiting anterior growth and encouraging posterior growth, ultimately leading to a reversal in the tibial slope. Similarly, the weight-bearing axis in crouch gait is typically shifted posteriorly behind the knee; thus, the growth of the posterior physis may be inhibited, leading to an increased posterior slope, as seen in the younger patients in our study. After the crouch gait is corrected, the weight-bearing axis is returned to a more neutral position, allowing the posterior growth plate to again grow longitudinally and encouraging a more anterior tibial slope (Fig. 3). Any one of these changes might result in a change in the tibial slope and could contribute to a premature apophyseal closure. While alternative methods to improve patella alta may minimize proximal tibial growth disturbances, including patellar tendon imbrication or patellar tendon shortening, data on the long-term durability of these alternative methods are currently unavailable, and the authors have no experience with this technique [13].

Fig. 3 Illustration of the forces crossing the proximal tibial physis before and after patellar tendon advancement. Prior to patellar tendon advancement, the patellar tendon and the posterior weight-bearing axis create an tensile anterior load and a compressive posterior load, contributing to a more posterior tibial slope. After the patellar tendon has been advanced and the weight-bearing axis is shifted to a more anterior position, a compressive anterior force and tensile posterior force may promote a more anteriorly directed tibial slope

One important question is “When does the slope reversal become problematic?” Obviously, an extreme reversal in slope would lead to a recurvatum deformity and potentially an unstable, back-kneed gait. However, a slight slope reversal might be beneficial to a child with crouched gait and in effect may be similar to a distal femoral extension osteotomy. Looking only at our average slope values, this hypothesis could be argued (Tables 4, 5). Our final posterior slopes in the younger children are not statistically different from the initial slopes in the older patients or from those of the aged-matched controls. In seven of nine patient knees, however, we observed anterior apophyseal closure with an open growth plate, which the authors feel will continue to worsen. Figure 2 is an example of one patient in the study who demonstrated complete growth plate closure at follow-up. It was assumed that this closure was preceded by a premature apophyseal closure and reversal of posterior tibial slope following patellar tendon advancement. As the fusion of the anterior growth plate inhibited growth of the anterior physis and the posterior growth plate continued to grow, this patient’s tibial slope became more anteriorly directed.

Another question that remains is “Why do we see such a change in children <11 versus those ≥11 years old, despite both groups having open physes?” Both groups showed premature apophyseal closure and a significant decrease in posterior slope, but a much more significant change (10° vs. 3°) was seen in those patients aged <11 years over the same time period. We still do not have an answer for this. Additionally, it may be useful for future studies to evaluate the gender differences as it relates to the age differences seen in this study, as females mature earlier than males, and the time to delay surgery may be affected.

While our findings are the first to show the effects of patellar tendon advancement on the tibial physis in the immature patient, there are significant limitations to our study. The first of these is the low number of subjects enrolled in the study. The authors were limited by the number of these procedures performed at our institution and the inclusion criteria. Second, the short-term follow-up may also be seen as a potential limitation; however, the short duration of the follow-up may actually highlight the significance of these findings. At only an average of 19 months of follow-up, we demonstrate significant changes in the tibial slopes. The natural history of physeal injuries would lead one to believe these will only worsen over time. If the slopes continue to change to a point that is either clinically noticeable via back kneeing or radiographically unacceptable (perhaps past neutral), the authors feel it would be unethical to not intervene. From the average rate of change found in this study (10° at 1.6 years), this could occur within 1–2 years of additional follow-up. Furthermore, at the time of review one patient had required operative intervention for this change in slope and surgery was being discussed with a second. Thus, two of the nine patients were found at 1.6 years follow-up to have what the authors feel to be clinically significant recurvatum. Other limitations of this study include the use of retrospective lateral radiographs that were not obtained for the purpose of assessing the tibial physis or tibial slope, making radiographic analysis more difficult. We attempted to minimize the variability in these measurements by performing them three times by a single reader for both the patients and the age-matched controls.

In conclusion, the tibial slope of younger patients with crouch gait had a greater initial posterior tibial slope than control patients of the same age and sex. Advancement of the patellar tendon to a site distal to the proximal tibial physis appears to result in premature apophyseal closure and thus a change in the tibial slope to a more anterior direction. While this was seen overall in our patients, those children aged <11 years appeared to be most susceptible. Close clinical follow-up supplemented with lateral radiographs for assessing tibial slope is recommended in these patients following patellar tendon advancement. The surgeon may want to wait until the child is older than 11 years before performing this procedure.

Conflict of interest

None.

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