Abstract
Background
Proximal femur guided growth (PFGG) is a minimally invasive treatment option for coxa valga and hip displacement in cerebral palsy (CP). Its role in hypotonic CP remains unclear. This study evaluated PFGG as a potential intermediate surgical option between observation and reconstructive osteotomy for hypotonic hip coverage deficiency.
Methods
This retrospective study reviewed children with hypotonic CP who received PFGG for hip acetabular coverage deficiency from 2012 to 2021. Surgical indications included a head-shaft angle (HSA) greater than 155° and a Reimers’ migration percentage (MP) greater than 30%. The MP, HSA, and acetabular index were measured on serial radiographs. A decrease or increase in MP by 5 percentage points or more postoperatively was considered clinically significant. Adverse events, revision PFGG, and reconstructive procedures were recorded.
Results
Fourteen patients (25 hips) underwent PFGG without concomitant soft-tissue releases at a mean age of 5.3 years (standard deviation: 2.3). The HSA improved significantly from 175.7° preoperatively to 165.3° at 2 years and 163.0° at the latest follow-up (mean: 50.4 months; P < .001). However, MP showed no significant change (41.2% preoperatively, 40.6% at 2 years, 40.7% at 4.2 years). Among the 12 hips with a preoperative MP of 30%-40%, MP decreased from 34.5% to 31.9%, and all hips were maintained below 40%. In contrast, among the 13 hips with a preoperative MP greater than 40%, subsequent procedures were required, including revision PFGG, femoral varus osteotomy, and pelvic osteotomy.
Conclusions
PFGG significantly decreased coxa valga but did not reliably affect MP or acetabular coverage. While it may provide a low-morbidity, intermediate surgical treatment option for selected hypotonic CP hips with coxa valga, further research is warranted to assess its clinical effectiveness.
Key Concepts
-
(1)
Proximal femur guided growth demonstrated a limited effect on reducing hip displacement in hypotonic cerebral palsy despite coxa valga improvement.
-
(2)
Guided growth may offer a more active treatment option than observation alone.
-
(3)
Early application of proximal femur guided growth is recommended for hips with a migration percentage <40% to prevent progression of hypotonic hip displacement.
Level of Evidence
Level IV, case series study
Keywords: Cerebral palsy, Hypotonia, Hip displacement, Guided growth, Coxa valga
Introduction
Hip displacement is a common musculoskeletal disorder in patients with cerebral palsy (CP) [1,2]. Without treatment, it often progresses to dislocation [1,3,4], leading to chronic arthritis and reduced quality of life in hypertonic patients. Myofascial releases, femoral osteotomy, and acetabuloplasty are commonly used to improve hip motion and prevent dislocation [5,6]. However, these treatments remain controversial in patients with hypotonia. In hypotonic patients, hip motion is often preserved, with no fixed adduction contracture and sufficient flexion, abduction, and rotation for sitting, hygiene, and positioning [7]. Therefore, soft-tissue releases directed at the adductors, iliopsoas, and hamstrings are not routinely indicated unless contracture or positioning difficulty is present. Nonetheless, hip displacement can still progress [7], especially in patients who are initially hypotonic but develop increased muscle tone later.
Hip surveillance is widely recommended to detect hip displacement at an early stage. For hypotonic hips with flexible motion and mild to moderate coverage deficiency, observation alone may permit continued radiographic progression, whereas reconstructive osteotomy may be considered disproportionate if the child is asymptomatic and the hip remains reducible. PFGG using a single eccentric screw has been reported as a less invasive treatment option to correct coxa valga, decrease migration percentage (MP) [[8], [9], [10], [11], [12], [13], [14], [15]], and prevent recurrence of displacement in spastic hip displacement [16]. Given its minimally invasive nature, PFGG may be a viable treatment to address the coxa valga that is a common skeletal pathology in patients with hypotonic CP.
This study aims to evaluate the effectiveness of PFGG without soft-tissue release in treating hypotonic hip displacement. By analyzing changes in head-shaft angle (HSA), MP, and acetabular index (AI) over time, we aim to provide valuable insights into the efficacy of this approach for this specific patient population.
Material and methods
Patient selection and study design
Patients were selected from a single tertiary center and included if they met all of the following criteria: (1) diagnosis of hypotonic CP; (2) PFGG performed as the initial surgical treatment for hip coverage deficiency between 2012 and 2021; (3) coxa valga, defined as HSA greater than 155°; (4) a Reimers’ MP [17] greater than 30%; and (5) minimum postoperative follow-up of 2 years with serial anteroposterior pelvic radiographs. This HSA threshold was selected because it represents coxa valga, the femoral deformity targeted by PFGG, and has been used in prior PFGG studies [10,12,16]. Patients were excluded if they had previous hip reconstruction, concomitant adductor, iliopsoas, or hamstring release, concomitant osteotomy, or inadequate radiographs for measurement. Because the institutional data set for this preliminary report was generated from a procedure-based retrospective database, the denominator of hypotonic CP patients who underwent hip surveillance but did not receive PFGG during the same period could not be reliably determined. The flowchart of patient inclusion and exclusion is summarized in Fig. 1. Surgical indication was hip coverage deficiency rather than fixed contracture. Reconstructive surgery was indicated when the MP was greater than 50% or when rapid progression was observed on serial surveillance; for this study, rapid progression was defined as an increase in MP greater than 10 percentage points within 12 months or progressive subluxation with loss of containment (Fig. 1).
Figure 1.
Flowchart of patient inclusion and exclusion. HSA, head-shaft angle; MP, migration percentage.
Surgical technique
The patient was placed in the supine position. Femoral anteversion was determined by internally rotating the femur until the longest femoral neck projection was shown under fluoroscopy. With the femoral neck parallel to the table, a guide wire was placed from the posterolateral femoral cortex toward the center of the capital epiphyseal plate and into the medial half of the capital epiphysis. To view the proximal femur on a lateral projection, the leg was placed in flexion and external rotation, and the guide wire was confirmed to lie along the central axis of the femoral neck. Intraoperative fluoroscopy was used throughout guidewire positioning, reaming, tapping, and the final screw placement. If the screw threads did not approach the osseous margin of the capital epiphysis while remaining safely extra-articular, the screw was advanced under repeated anteroposterior and lateral fluoroscopic confirmation. After reaming and tapping along the guide wire, a 7.0-mm stainless steel cannulated screw (Synthes Inc., West Chester, PA, USA) was inserted until the threads touched the osseous margin of the capital epiphysis, with as many threads in the epiphysis as safely possible. In children younger than 7 years, a 4.5-mm cannulated screw was used [10,12,16]. Screw replacement or revision PFGG was part of our institutional treatment strategy throughout the study period and was considered when the capital epiphysis outgrew the screw while residual MP remained greater than 40%. No abduction brace or spica cast was used postoperatively in these hypotonic patients. Motion and full weight-bearing were allowed. Clinical follow-up was conducted every 6 months.
Data collection and statistics
A retrospective chart review was conducted to collect patient demographics, including age, sex, and functional levels, as described by the Gross Motor Function Classification System (GMFCS), hip range of motion, and subsequent procedures. The main outcome measures were correction of coxa valga [18,19] and change in hip coverage deficiency. Preoperative radiographs of the pelvis and postoperative radiographs at 6 months, 1 year, 2 years, and the final follow-up were analyzed to assess changes in MP, HSA, and AI. The MP was calculated as the percentage of the femoral capital epiphysis lateral to the acetabular edge. The HSA was measured by the angle between the line perpendicular to the capital epiphyseal plate and the axis of the femoral shaft. We used the HSA rather than the neck-shaft angle because the HSA is less sensitive to malrotation of the femur on radiographs and represents deformities of caput valgum and coxa valga [19]. The AI was measured as the angle between the Hilgenreiner line and the line connecting the lateral edge of the acetabular saucer to the inferior pole of the ilium. One author performed all radiographic measurements, which were subsequently reviewed by the senior author. Measurements with uncertainty were reassessed until consensus was reached.
Paired t-tests were used to compare outcomes between the preoperative condition and those at 2 years postoperatively. A change in MP of more than 5 percentage points, either increase or decrease, was considered clinically significant. Hips were stratified by a preoperative MP of <40% or ≥40% to evaluate treatment effects. As this retrospective preliminary study included all eligible patients treated during the study period, an a priori sample size calculation was not feasible. Given the small cohort size, the statistical analyses were considered exploratory and were interpreted together with individual radiographic trajectories. Statistical analyses were performed using SAS version 9.2 (SAS Institute Inc., Cary, NC, USA) and Microsoft Excel 2017 (Microsoft Corp., Redmond, WA, USA). A two-tailed P value less than 0.05 was considered statistically significant.
Results
Fourteen consecutive patients with hypotonic CP who underwent PFGG in 25 hips were included in the study. The average age at the time of surgery was 5 years and 4 months (range: 3.2-11.2 years). The cohort included 8 boys and 6 girls. Their functional levels were GMFCS level III in 6, level IV in 6, and level V in 2 children. The average follow-up period was 50.4 months postoperatively (range: 28-80 months).
The primary outcome measure of the effectiveness of PFGG was the change in coxa valga. The mean HSA decreased from 175.7° preoperatively to 165.3° at 2 years postoperatively (P < .001) and further to 163.0° at the final follow-up (P < .001) (Table 1). The mean MP was 41.2% preoperatively, 40.6% at 2 years postoperatively, and 40.7% at the latest follow-up (Table 2). The AI remained relatively stable throughout the follow-up period, with mean preoperative values of 23.6° and 23.2° at the latest follow-up (Fig. 2).
Table 1.
Data of the head-shaft angle in the 25 hips stratified by operation age.
| Case no. (GMFCS) | Age (years) | Side | Preoperative | 1 y | 2 y | Latest follow-up |
|---|---|---|---|---|---|---|
| Case 1 (IV) | 3.2 | R L |
179.5 179.9 |
169.3 170.2 |
160.1 162.6 |
160.1 (24 mo) 162.6 |
| Case 2 (IV) | 3.3 | R L |
179.0° 178.0° |
177.9° 178.0° |
177.0° 176.8° |
177.0° (46 mo) 179.0° |
| Case 3 (III) | 3.6 | R L |
175.0 178.3 |
171.2 172.2 |
170.0 172.5 |
170.0 (24 mo) 172.5 |
| Case 4 (III) | 4.0 | R L |
173.6° 179.0° |
172.4° 170.1° |
167.0° 168.4° |
156.6° (62 mo) 167.7° |
| Case 5 (V) | 4.1 | R L |
179.0° 179.4° |
171.3° 177.4° |
157.0° 175.4° |
166.7° (40 mo) 170.8° |
| Case 6 (III) | 4.4 | R L |
178.3° 176.5° |
178.0° 170.1° |
177.8° 170.8° |
162.3° (57 mo) 162.2° |
| Case 7 (IV) | 5.0 | R L |
166.1 173.9 |
167.8 168.0 |
164.3 164.4 |
166.0 (31 mo) 162.9 |
| Case 8 (III) | 5.2 | L | 168.6° | 164.2° | 160.9° | 150.5° (58 mo) |
| Case 9 (III) | 5.2 | R L |
166.4° 179.3° |
171.0° 172.4° |
171.8° 165.2° |
174.0° (70 mo) 169.2° |
| Case 10 (IV) | 6.6 | R | 179.0° | 178.0° | 169.7° | 165.0° (80 mo) |
| Case 11 (IV to III) | 6.8 | R L |
174.5° 178.0° |
176.4° 176.1° |
162.2° 161.6° |
143.6° (77 mo) 153.3° |
| Case 12 (IV) | 6.9 | R L |
173.1° 176.5° |
167.2° 155.6° |
162.4° 150.8° |
165.1° (38 mo) 154.0° |
| Case 13 (V) | 9.2 | R L |
173.7° 173.6° |
165.1° 166.6° |
158.2° 155.8° |
157.7° (44 mo) 155.0° |
| Case 14 (III) | 11.2 | L | 175.8 | 165.1 | 155.4 | 155.9 (55 mo) |
| Average | 175.7 | 170.9 | 165.3 | 163.0 (50.4 mo) |
GMFCS, Gross Motor Function Classification System.
Table 2.
Data of the migration percentage (%) and subsequent surgeries.
| Case no. (GMFCS) | Side | Preoperative (%) | 1 y (%) | 2 y (%) | Latest follow-up | Subsequent surgeries |
|---|---|---|---|---|---|---|
| Case 1 (IV) | R L |
32.0 36.4 |
33.1 35.7 |
35.7 36.2 |
35.7 (24 mo) 36.2 |
|
| Case 2 (IV) | R L |
40.0 45.0 |
42.1 43.0 |
43.9 44.0 |
40.5 (46 mo) 50.0 |
Revision PFGG Femur varus osteotomy |
| Case 3 (III) | R L |
57.6 50.3 |
54.9 46.7 |
55.7 45.3 |
55.7 (24 mo) 45.3 |
|
| Case 4 (III) | R L |
51.0 31.7 |
47.8 36.4 |
44.0 39.3 |
33.2 (62 mo) 38.0 |
Revision PFGG |
| Case 5 (V) | R L |
51.0 44.0 |
46.7 43.6 |
41.0 43.4 |
42.3 (40 mo) 46.4 |
|
| Case 6 (III) | R L |
36.7 30.5 |
35.9 33.2 |
31.9 32.5 |
29.3 (57 mo) 32.0 |
|
| Case 7 (IV) | R L |
36.6 34.0 |
36.1 35.1 |
35.5 32.6 |
34.0 (31 mo) 30.0 |
|
| Case 8 (III) | L | 30.0 | 28.0 | 29.0 | 28.2 (58 mo) | |
| Case 9 (III) | R L |
43.5 35.3 |
42.1 33.8 |
47.1 29.5 |
50.1 (70 mo) 20.1 |
Revision PFGG |
| Case 10 (IV) | R | 51.9 | 44.1 | 45.0 | 49.2 (80 mo) | Revision PFGG |
| Case 11 (IV to III) | R L |
44.8 42.7 |
52.3 42.1 |
47.1 40.4 |
47.1 (77 mo) 52.1 |
Revision PFGG |
| Case 12 (IV) | R L |
44.1 44.6 |
43.2 56.3 |
42.1 68.6 |
40.8 (38 mo) 69.4 |
Triple osteotomy |
| Case 13 (V) | R L |
39.9 33.5 |
38.0 28.4 |
37.1 28.4 |
36.3 (44 mo) 27.4 |
|
| Case 14 (III) | L | 33.2 | 34.5 | 33.6 | 38.4 (55 mo) | |
| Average | 41.2 | 40.8 | 40.6 | 40.7 (50.4 months) |
GMFCS, Gross Motor Function Classification System; PFGG, proximal femur guided growth.
Figure 2.
The changes in the (A) head-shaft angle (HSA) and (B) migration percentage (MP) over the 2 years after PFGG.
The individual effects on the MP were variable and unrelated to gross motor function or age. At 2 years postoperatively, MP decreased by more than 5% in 6 hips, remained as preoperative condition in 17 hips, and increased by more than 5% in 2 hips. The 6 hips with improvement were from 3 patients with GMFCS level III and 3 patients with GMFCS level IV or V. Their ages at the time of surgery were 3.6, 4.0, 4.1, 5.2, 6.6, and 9.2 years, respectively (Fig. 3). The 2 hips with deterioration were from 2 patients with GMFCS levels III and IV, aged 4.0 and 6.9 years, respectively, at the time of surgery.
Figure 3.
(A) A 4.4-year-old boy (case 6) with right hip displacement (MP—R: 36.7%, L: 30.5%; HSA—R: 178.3°, L: 176.5°) underwent bilateral PFGG (B). (C) By the age of 10.0 years, coxa valga and hip displacement had been corrected (MP—R: 29.3%, L: 32.0%; HSA—R: 162.3°, L: 162.2°). HSA, head-shaft angle; MP, migration percentage; PFGG, proximal femur guided growth.
At the latest follow-up, 4.2 years postoperatively, 5 patients received revision PFGG. The capital epiphysis outgrew the screw at a mean of 19.3 months after the index procedure, and revision PFGG was performed at a mean of 24.5 months for a residual MP greater than 40%. Two patients underwent reconstructive surgery. One patient (case 2) had worsening hip displacement from an MP of 45% to an MP greater than 50% after revision PFGG and received femoral varus osteotomy 3.8 years after the initial guided growth procedure. Another patient (case 12) received open reduction and pelvic triple osteotomy for progressive hip subluxation from an MP of 45% to an MP of 69% 3.2 years after guided growth. One patient (case 9), who was initially hypotonic, later developed asymmetric muscle tone and a windblown posture. Hip displacement worsened quickly, and reconstructive surgery was indicated but was not accepted by the family.
The 25 hips were stratified according to the preoperative MP of no more than 40% and greater than 40% to evaluate surgical outcomes at the latest follow-up. Among the 12 hips with a preoperative MP of 30%-40%, the mean MP decreased from 34.5% to 31.9%, and all hips were maintained below 40%. In contrast, among the 13 hips with a preoperative MP >40%, 3 required reconstructive surgery because of progressive displacement, with the MP increasing to >50% (Table 2).
Discussion
This retrospective preliminary study of patients with hypotonia demonstrated that PFGG without concomitant soft-tissue releases had a limited effect on reducing MP, in contrast to its significant effect on correcting coxa valga. Importantly, PFGG did not reliably improve acetabular coverage and should not be considered a substitute for reconstructive hip surgery in advanced subluxation. However, in hips with an MP less than 40%, PFGG may help reduce coxa valga through a minimally invasive procedure.
The mechanism of hip displacement in hypotonia differs from that in hypertonia. The typical imbalance between hip adductor and abductor muscle forces seen in spastic hip displacement is absent or less prominent. Instead, generalized muscle weakness, delayed or abnormal weight bearing, coxa valga, and insufficient acetabular development appear to contribute to progressive lateralization of the femoral head [7]. These hips may retain flexible motion, but subluxation may continue because of acetabular insufficiency and coxa valga. PFGG effectively induced coxa vara and stabilized the hip in a nonsubluxated state. However, because acetabular deficiency was not directly corrected, MP and AI often remained pathologic. This finding may support the use of PFGG in the early stages of hip subluxation (Fig. 4).
Figure 4.
A 6.8-year-old boy (case 11) with bilateral hip displacement (A) underwent PFGG. The right hip screw was initially placed too medially (B), requiring revisional guided growth 2 years later (C). At the age of 14.1 years, the hip remained reduced (D), although the MP values were 47% in the right hip and 52% in the left hip, owing to insufficient acetabular roof. MP, migration percentage.
The goal of hip surveillance is to detect and manage hip displacement at an early stage. Miller [7] followed up 53 patients with GMFCS levels II to V over a period of 3-8 years, and 14 hips demonstrated progression of displacement. Patients with hypotonic CP are also at risk of progressive hip displacement (Fig. 5). PFGG may serve a therapeutic role by correcting coxa valga and stabilizing the hip, bridging the gap between observation for mild hip displacement and osteotomy for severe hip subluxation.
Figure 5.
A boy with hypotonic cerebral palsy (GMFCS level IV) demonstrating progressive hip displacement: (A) MP: 23.8% (right) and 35.6% (left) at 3.8 years; (B) MP: 41.5% (right) and 51.9% (left) at: 4.8 years; (C) MP: 54.6% (right) and 58.5% (left) at 5.8 years; and (D) MP: 50.0% (right) and 68.5% (left) at 6.8 years. Proximal femur guided growth may be beneficial if performed at the stages shown in (A) and (B). GMFCS, Gross Motor Function Classification System; MP, migration percentage.
Reconstructive hip surgery provides immediate correction of coxa valga and acetabular dysplasia and is the preferred treatment for advanced or rapidly progressive hip displacement. In contrast, PFGG is a growth modulation procedure designed to maintain a reduced, flexible, pain-free, albeit dysplastic, hip in hypotonic children with limited ambulatory function and may serve as an active alternative to observation for early-stage hip displacement detected through hip surveillance.
In this hypotonic cohort, the femoral capital epiphysis outgrew the guided growth screw in 5 of 14 patients. Because this study did not include a matched hypertonic CP cohort, we could not determine whether screw outgrowth was more frequent in hypotonic patients than in hypertonic patients. Potential contributing factors include poor epiphyseal bone quality associated with nonambulatory hypotonia and excessively eccentric screw placement. To address this issue, the screw was placed more centrally later in our practice, through an area of physis between the medial 40% and 50%, to achieve better purchase in the epiphyseal bone and prolong the effective duration of guided growth. However, this technical modification may also be a confounding factor because a more central screw could reduce the eccentric tethering effect and partly explain why MP did not improve consistently after the PFGG procedure.
A major limitation of this study is the absence of a matched untreated control group. The outcomes observed in hips with an MP of 30%-40% may partly reflect the natural nonprogressive course or motor development rather than the effect of guided growth alone. The number of hypotonic CP patients who underwent surveillance but did not undergo PFGG during the same period could not be reliably determined from the retrospective procedure-based database. A second limitation is the small sample size, which limited statistical power and prevented robust analysis of prognostic factors. This study is presented as a preliminary report. Ongoing recruitment, longer follow-up, and future comparison with matched observation or reconstruction cohorts are needed to determine the optimal indications for PFGG in hypotonic CP.
Conclusion
This preliminary report presents outcomes of PFGG in a small cohort of children with hypotonic CP. Although PFGG effectively corrected coxa valga, this did not result in a significant reduction in MP or improvement in AI because it does not directly address acetabular deficiency. Consequently, PFGG should not replace reconstructive hip surgery for advanced or rapidly progressive hip subluxation. With hip surveillance enabling early detection of mild displacement, guided growth may offer a more active treatment option over observation alone in preventing progression of hip subluxation.
Author contributions
Yutse Chang: Writing – original draft, Data curation. Szu Y. Wang: Formal analysis. Hsuan K. Kao: Project administration, Methodology. Chia H. Chang: Writing – review & editing, Supervision, Conceptualization.
Ethics approval and consent
This was a retrospective cohort study approved by the institutional review board of the authors’ hospital (institutional review board no.: 201900941B0). Written informed consent was waived due to the retrospective nature of the study.
Disclosure
No benefits, in any form, have been received or will be received from any commercial entity directly or indirectly related to the subject of this article.
Data availability
Patient data are available upon request.
Funding
No funding was received from the government for this study.
Declaration of competing interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors acknowledge that we used artificial intelligence (ChatGTP 5) to polish the English. The authors have read carefully the output from the model that was used, and the authors are fully responsible for the content of this work, including ensuring that the references accurately represent what is claimed here.
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Associated Data
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Data Availability Statement
Patient data are available upon request.