Population Characteristics

The patient populations were consistently limited to ambulant children with CP presenting with flexible spastic equinovarus deformity across the seven included studies. Patients who were non-ambulant and with fixed bony deformities were uniformly excluded. This is consistent with the indication of SPOTT for correctable soft tissue imbalance rather than rigid skeletal malalignment.

The total number of feet treated per study ranged from 13 to 146, with most studies evaluating cohorts between 25 and 140 feet. Mean age at surgery varied from 5.5 to 11 years. Follow-up durations ranged from 2.4 years to 10 years, with only three studies providing long-term data (> 7 years).

Sex distribution showed male predominance overall, although ratios varied. While some studies reported near-equal male-to-female representation, others demonstrated skewed distributions in either direction. Complete demographic breakdowns are summarized in Table 1.

Table 1 Demographic and surgicalcharacteristics of included studiesCerebral Palsy Subtypes

The following studies examined showed variability in the distribution of cerebral palsy (CP) subtypes; however, consistent trends were reported. Unless specified, the following percentages correspond to the proportion of patients rather than their feet. The only exception is Vlachou et al. [11] since the reported CP subtypes are based on the number of feet rather than the patients. Essentially, Vlachou et al. were excluded from Table 2 due to not converting the data to patient-level proportions. Spastic hemiplegia was the most prevalent subtype across nearly all studies, with a prevalence ranging from 69.2% (9/13) in Ahmed [6] to 75% (30/40) in Sayan [7]. Intermediate values were reported by Aleksic (2020) at 52.4% (65/124) and Mulier [14] at 59% (10/17). Spastic diplegia was the second most prevalent subtype. For instance, Ahmed reported 23.1% (3/13), 30.6% (38/124) in Aleksic, 12% (2/17) in Mullier, and 22.5% (9/40) in Sayan. Spastic quadriplegia was less frequently reported. For instance, Ahmed noted 7.77% (1/13), 12.1% (15/124) in Aleksic, and 29% (5/17) in Mulier. However, Sayan and Dussa did not report quadriplegia as a subtype. Finally, other subtypes were observed even less. Aleksic identified 4.8% (6/124) of patients as having spastic triplegia and 17.7% (22/124) as having spastic paraplegia. Sayan identified 2.5% (1/40) with triplegia but did not report paraplegia. Dussa [15] did not stratify patients by CP subtype.

Table 2 Reported frequencies of spastic cerebral palsy subtypes across studies

These Findings highlight the predominance of spastic hemiplegia and diplegia among surgical candidates for SPOTT. In contrast, quadriplegic and triplegic subtypes are generally associated with poorer outcomes. Essentially, the following trends highlight the importance of subtype-specific surgical planning and thorough preoperative functional assessment. A complete summary of CP subtype distribution by study is presented in Table 2.

An additional limitation is that Chang et al. [1] included patients undergoing both SPOTT and Z-lengthening procedures without reporting CP subtype by surgical group. Therefore, their data were excluded from Table 2, although subtype percentages were mentioned in the text.

Surgical Techniques Practiced

The reviewed studies investigated variations of the SPOTT technique for managing spastic equinovarus deformity in cerebral palsy. Aleksić et al. (2020) compared the standard SPOTT (per Green et al.) with a modified version incorporating Z-plasty elongation of the medial tibialis posterior (TP) tendon and a longitudinal split for improved balance, yielding superior outcomes. Chang et al. [1] utilized the standard SPOTT with Z-lengthening of the posterior tibialis. Mulier et al. [14] employed an anterior interosseous SPOTT, routing the tendon through the interosseous membrane to the dorsum, combined with Achilles tendon lengthening. Vlachou et al. [11] followed the Green et al. technique, making four incisions and transferring the tendon to the peroneus brevis via a posterior route. Sayan et al. [7] also utilized the Green method, detaching the plantar half of the tendon from the navicular, passing it posteriorly around the tibia and fibula, and securing it to the peroneus brevis via Pulvertaft weave. Ahmed et al. [6] employed a technique similar to Mulier, splitting the tibialis posterior and transferring the anterior half through the interosseous membrane to the lateral cuneiform, with concomitant percutaneous tendo-Achilles lengthening in all cases. Dussa et al. [15] used a combined SPOTT and SPLATT approach for flexible varus deformity, performing a posterior tibialis split transfer via the interosseous route to the peroneus brevis and anchoring with a Pulvertaft weave, as well as a split anterior tibialis transfer to the cuboid. These technique variations reflect ongoing refinements to improve tendon balance, foot progression angle, and long-term correction in this complex population.

Indications/Goals for Surgery

The rationale behind conducting SPOTT procedures in quadriplegic patients is focused on preventing complications rather than improving gait. Mulier et al. emphasized that SPOTT in quadriplegic patients helps prevent skin breakdown and pressure ulcers by correcting persistent equinovarus positioning, thereby improving tolerance for bracing and wheelchair use. Chang et al. further adds to this rationale by highlighting the benefits of facilitating standing, assisted walking, preventing contracture progression, and improving wheelchair positioning. However, Vlachou does not provide any explicit justification for including quadriplegic patients and their study reports high failure rates without analysis. Aleksić et al. reported similar findings, raising concern over outcomes and benefits in this subgroup. Overall, while SPOTT can offer improvements in positioning and caregiving tolerance, the decision to operate should be individualized, with goals centered on comfort rather than ambulation.

Initial Management

Pre-operative planning for SPOTT prioritizes the evaluation of flexible deformities and confirmation of ankle dorsiflexion. Patients with fixed bony deformities should undergo corrective bone procedures prior to tendon transfer to prevent persistent varus alignment. Common adjunctive procedures include plantar soft tissue release, aimed at lengthening the shortened base of the foot [11]. Additionally, modified surgical techniques, such as Z-plasty elongation of the posterior tibial tendon, have been employed to improve foot positioning and reduce recurrence risk [11].

Post-operative protocols also varied among studies. Sayan [7] implemented a structured plan involving three weeks of non–weight-bearing casting, followed by three weeks of weight-bearing casting, and then transition to a short ankle-foot orthosis (SAFO). This was paired with an intensive rehabilitation program focused on range of motion and strength. Surgical outcomes were assessed after one year using motion analysis to guide further bracing decisions [17].

Similarly, Ahmed [6] used an above-knee plaster cast with the ankle in a neutral position, permitting touchdown weight-bearing after three weeks. At six weeks, patients transitioned to an ankle-foot orthosis (AFO), which was continued for six months. Patients with favorable outcomes were advised to continue night splinting, while those with unsatisfactory results were considered for further surgical intervention, including calcaneocuboid fusion 18 months postoperatively [16].

Overall Recurrence and Failure

Across the reviewed studies, failure and recurrence rates following SPOTT procedures varied significantly, often reflecting inconsistencies in how these outcomes were defined and reported. While some studies provided explicit criteria for failure or recurrence, others relied on indirect or inferred definitions. A summary of the failure definitions and corresponding failure rates across all included studies is presented in Table 3. Aleksic et al. (2020) reported a failure rate of 19.9% (29/146 feet), defining failure as either a poor clinical outcome or the need for revision surgery, including triple arthrodesis. The highest failure rates in their cohort were seen in patients with GMFCS level IV (90.9%) and spastic quadriplegia (86.7%), compared to lower rates in GMFCS III (30.2%) and spastic diplegia (31.0%). Chang et al. [1] used a more specific definition—postoperative hindfoot deformity ≥ 10° in varus or valgus or the need for reoperation—and reported a failure rate of 44.3% (39/88 feet). Failures were more common in younger patients (< 8 years), non-ambulators, and those with quadriplegia (75% failure in 16 feet). Dussa [15] defined failure as either overcorrection (hindfoot valgus/flatfoot) or undercorrection (persistent varus), with a failure rate of 30.8% (4/13 feet). Sayan [7] inferred failure from postoperative foot progression angle falling outside the desired range (0–10° of external rotation) and reported a 50% failure rate (22/44 feet). Failures were linked to inconsistent surgical technique, untreated deformities, and tendon retraction. In contrast, Ahmed [6] and Mulier et al. [14] reported lower failure rates of 11.8% (2/17) and 9.5% (2/21), respectively, though both studies lacked explicit failure definitions. In these cases, failure was inferred from persistent deformity or technical error such as poor tendon tensioning or misidentification of the dominant deforming muscle. Vlachou et al. [11] similarly lacked a formal definition but reported a 10.5% failure rate (4/38 feet), with failure generally interpreted as recurrence requiring further intervention.

Table 3 Definitions of recurrence and failure across included studies

Overall, the definitions of both recurrence and failure across the literature remain heterogeneous. Some studies used radiographic or angular thresholds, while others relied on clinical judgment, revision surgery, or the presence of complications such as pain or callosities. This inconsistency poses a significant barrier to data synthesis and cross-study comparisons and underscores the need for a standardized definition to guide both clinical evaluation and research reporting (see Table 3).

Patient-Specific Risk Factors for Failure

Several patient-specific factors have been consistently linked with higher failure and recurrence rates following split posterior tibialis tendon transfer (SPOTT) in children with cerebral palsy, however, the strength of statistical evidence varies across studies, as shown in Table 4. It was reported that patients under 8 years old were the most frequently identified risk factor. This link was addressed in at least four studies [6, 13, 15, 20]. Chang et al. [1] [6] found a significant increase in failure rates in children under 8. Essentially, Chang et al. [1] [6] reported a 61% failure rate (p < 0.05) in this group. In addition, Aleksic et al. (2020) [13] and Vlachou et al. (2010) [11], came to a similar conclusion. They reported higher recurrence rates among younger patients, however neither conducted formal statistical testing. Furthermore, Mulier et al. [14] also noted age-related recurrence but did not provide a statistical analysis of their data.

Table 4 Summary of Patient-Specific and surgical risk factors associated with failure of split posterior tibialis tendon transfer (SPOTT) in children with cerebral palsy

In contrast, older patients over 16 years old, were found to have a higher failure rate, potentially due to the reduced joint adaptability and the presence of more rigid deformities. This finding was reported by Mulier et al. [14], although no statistical evidence was provided.

Additionally, the cerebral palsy subtypes were another major factor in the clinical outcome. For instance, Chang et al. [1] [6] reported increasing failure rates were linked with neurological severity: 23% in spastic hemiplegia, 52% in diplegia, and 66% in quadriplegia, with a statistically significant difference (p = 0.004). Likewise, Vlachou et al. (2010) [11] reported significantly poor outcomes in diplegic and quadriplegic patients compared to hemiplegics (chi-square, p = 0.005), thereby highlighting the link between CP severity and SPOTT outcomes.

The preoperative ambulatory function has been shown to be a major factor in surgical outcomes. For instance, both Chang et al. [6] and Aleksic et al. [13] reported that patients with limited or no ambulation had significantly higher failure rates, with values reaching up to 79% compared to 23% in ambulatory patients (p < 0.01). Essentially, the following findings support the notion of baseline functional status and serve as a valuable prognostic indicator.

Other patient-specific risk factors have been reported with limited statistical data. Ahmed et al. [16] identified severe preoperative deformity— Characterized by equinus greater than 25° or varus greater than 20°—along with marked Achilles tendon contracture as a significant factor in poor correction outcomes; however, they do not provide statistical data to corroborate these findings. Mulier et al. [14] noted that limited preoperative hindfoot mobility appeared to restrict postoperative correction, while Vlachou et al. [11] highlighted the necessity of addressing proximal alignment issues such as femoral or tibial torsion, to limit residual deformity. Nevertheless, these factors were discussed qualitatively, without statistical analysis, making it difficult to gauge their impact.

In conclusion, younger age, greater severity of cerebral palsy (CP), and poor baseline ambulation have been statistically associated with poor outcomes of SPOTT. However, numerous other risk factors remain within the studies. This highlights the importance of future multivariate analyses to better quantify their relative influence.

Surgical Risk Factors for Failure

The surgical technique represents a crucial factor in influencing the success of SPOTT, as shown in Table 4. The most commonly reported surgical technique complication was inadequate tensioning of the tendon, which may have caused an under-correction or overcorrection of the deformity. This complication was reported in three studies [13,14,15]; however, none of the following studies conducted statistical analysis that linked tensioning errors with surgical outcomes.

Another contributing factor to under-correction is the misidentification of the dominant muscle responsible for the deformity, especially in cases involving mixed or atypical deformity patterns [16]. However, no statistical evidence was provided.

Additional factors contributing to recurrences, such as tendon retraction and insufficient tendon lengthening were reported in both Sayan [7] and Vlachou [11]. Sayan et al. further highlighted that inter-surgeon variability in technique was a major factor in inconsistent surgical outcomes. However, statistical evidence was not provided.

In conclusion, the modes of failure varied across studies such as under-correction, over corrections (into hindfoot valgus or flatfoot), persistent varus deformity, and the need for revision surgeries such as triple arthrodesis of calcaneocuboid fusion. Despite these findings, the majority of the reports addressing surgical risk factors remain largely descriptive, with very few studies providing statistical evidence for technical complications to surgical failures.

Management of Failure

Various strategies have been proposed for addressing failure or recurrence following SPOTT. These approaches include continued bracing, revision surgeries and additional procedures individualized to the specific nature of the recurrence. Aleksic et al. emphasized that revision surgeries, specifically triple arthrodesis, are frequently performed on patients who developed recurrent equinovarus or overcorrected into valgus deformity.

In addition, Vlachou highlighted the importance of bracing and additional corrective surgeries, such as calcaneocuboid fusion, for severe recurrences. Furthermore, Chang recommended repeating tendon lengthening for cases of recurrent varus, while patients presenting with significant valgus deformities were managed with an ostomy or subtalar arthrodesis. Several studies have highlighted that the management of failure typically involves a combination of prolonged bracing, surgical revisions, and targeted procedures, depending on the deformity.

Study-Level Bias

Bias was consistently identified in all studies as a result of retrospective methodologies, absence of blinding, and irregular outcome reporting [6, 11, 13, 14, 17]. Selection bias was introduced due to non-random patient inclusion, with additional distortion caused by excluding non-ambulatory patients or individuals with fixed deformities [11, 14, 17]. Attrition bias was especially evident in Vlachou, where fewer than 50% of qualified patients were present at the final follow-up without analyzing those who were lost [11], and in Aleksic, which documented 8% of missing data with no imputation [13]. In Sayan, the omission of patients undergoing bony rotational procedures might have skewed the sample towards simpler deformities [17]. Performance bias might be present in all studies because of various surgeons and differing perioperative protocols, which were neither standardized nor reported comprehensively. Detection bias was probable in Mulier and Vlachou, as they predominantly depended on unblinded, subjective clinical evaluations lacking objective measures [11, 14]. Reporting bias was apparent in all studies, particularly with the consistent lack of patient-reported outcome measures [11, 14, 17], hindering the assessment of functional benefits from the patient’s viewpoint.