Predicting Allograft Volume in Orthopedic Oncology: Hemielipsoid Formula vs Intraoperative Fluid-Fill Measurement (PREDALL)

Preoperative Bone Defect Volume Estimation Using the Hemielipsoid Formula for Allograft Planning in Musculoskeletal Tumor Surgery: A Prospective Validation Study Against Intraoperative Fluid Displacement Measurement

Bone defects following primary musculoskeletal tumor resection are frequently reconstructed using structural allografts. Allograft availability is limited, and intraoperative waste due to oversized graft selection remains a practical challenge in orthopedic oncology. Accurate preoperative estimation of the expected defect volume is therefore critical not only for surgical planning but also for minimizing unnecessary allograft use.

This prospective study aims to evaluate the accuracy of the preoperative hemielipsoid formula in estimating bone defect volume after primary musculoskeletal tumor resection, using intraoperative fluid displacement as the reference standard. A secondary aim is to determine whether preoperative CT-based hemielipsoid volume calculation can reliably guide allograft selection and reduce intraoperative graft waste.

Patients scheduled for primary musculoskeletal tumor resection with structural allograft reconstruction at Sakarya University Training and Research Hospital will be enrolled. Preoperative defect volume will be estimated using the hemielipsoid formula (V = 4/3 × π × a × b × c / 2) derived from preoperative CT measurements. Intraoperative defect volume will be measured by fluid displacement as the reference standard. Agreement between methods will be assessed by Bland-Altman analysis and intraclass correlation coefficient (ICC).

Study Overview

• Status: Active, not recruiting
• Conditions: Bone Neoplasms; Bone Transplantation; Musculoskeletal Neoplasms
• Intervention / Treatment: Procedure: Hemielipsoid Formula-Based Preoperative and Intraoperative Bone Defect Volume Estimation

Detailed Description

**Background:** In orthopedic oncology, structural allograft reconstruction following primary musculoskeletal tumor resection requires precise preoperative planning. Currently, allograft selection at our institution relies on the surgeon's intraoperative visual estimation, with no standardized preoperative volumetric assessment protocol in place. This approach may result in allograft waste due to oversized graft selection, which is particularly problematic given the limited availability of allograft bank resources.

**Rationale:** The hemielipsoid formula (V = 4/3 × π × a × b × c / 2) offers a simple, reproducible method for estimating irregular bone defect volumes from standard cross-sectional imaging. If validated against an intraoperative reference standard, this formula could serve as a practical preoperative planning tool to guide allograft selection and minimize unnecessary graft use.

**Study Design:** This is a single-center prospective observational study conducted at Sakarya University Training and Research Hospital, Department of Orthopedics and Traumatology.

**Preoperative Assessment:** Defect volume will be estimated by the operating surgeon using the hemielipsoid formula applied to routine preoperative CT imaging. The three principal dimensions of the anticipated resection defect (length, width, and depth) will be measured on axial, coronal, and sagittal CT reconstructions, and volume will be calculated accordingly.

**Intraoperative Assessment:** Following tumor resection, the actual bone defect volume will be measured by direct cavity fluid displacement as the intraoperative reference standard. The resection cavity will be filled with a measured volume of saline to determine the true defect volume.

**Outcome Assessment:** The primary outcome is the agreement between preoperative hemielipsoid-estimated volume and intraoperative fluid displacement-measured volume, assessed by Bland-Altman analysis and intraclass correlation coefficient (ICC). The secondary outcome is the correlation between preoperative volume estimation and actual allograft volume used, to evaluate the utility of the hemielipsoid formula in reducing intraoperative allograft waste.

**Sample Size:** A priori power analysis was performed based on intraclass correlation coefficient (ICC) estimation (H0: ICC = 0.70; H1: ICC = 0.90; two-tailed alpha = 0.05; power = 0.80) using the Fisher z-transformation method, indicating a minimum required sample size of 25 patients. Target enrollment was set at 40 patients to account for a 10% dropout rate and to allow for potential subgroup analyses.

• Study Type: Observational
• Enrollment (Estimated): 40

Contacts and Locations

Study Locations

• Turkey (Türkiye)
  • Sakarya, Turkey (Türkiye)
    • Sakarya University Training and Research Hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

Patients scheduled for primary musculoskeletal tumor resection with structural allograft reconstruction at the Department of Orthopedics and Traumatology, Sakarya University Training and Research Hospital. All patients are evaluated by a multidisciplinary oncology team prior to surgical planning.

Description

Inclusion Criteria:

1. Patients diagnosed with a primary musculoskeletal tumor requiring surgical resection
2. Structural allograft reconstruction planned following resection
3. Routine preoperative CT imaging available for hemielipsoid measurements
4. Age ≥ 18 years
5. Written informed consent obtained

Exclusion Criteria:

1. Metastatic bone tumors
2. Pathological fracture at the resection site precluding accurate volume estimation
3. Prior surgery at the same anatomical site
4. Unavailability of adequate preoperative CT imaging
5. Reconstruction planned with implant or autograft only (no structural allograft)

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort

Intervention / Treatment

Hemielipsoid Volume Estimation Group; atients undergoing primary musculoskeletal tumor resection with structural allograft reconstruction. Preoperative bone defect volume is estimated using the hemielipsoid formula from CT imaging. Intraoperative defect volume is measured by saline cavity fill displacement as the reference standard.

Procedure: Hemielipsoid Formula-Based Preoperative and Intraoperative Bone Defect Volume Estimation; Preoperative bone defect volume is estimated by the operating surgeon using the hemielipsoid formula (V = 4/3 × π × a × b × c / 2) applied to routine preoperative CT imaging. The three principal dimensions of the anticipated resection defect are measured on axial, coronal, and sagittal CT reconstructions. Intraoperative defect volume is measured by saline cavity fill displacement as the reference standard. No additional procedures beyond standard surgical care are performed.; Other Names: Fluid Displacement Intraoperative Measurement

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Agreement between preoperative hemielipsoid-estimated and intraoperative fluid displacement-measured bone defect volume	Assessed by Bland-Altman analysis and intraclass correlation coefficient (ICC) between the two volumetric measurement methods	Intraoperative (Day 1)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Allograft waste volume	Difference between allograft volume prepared and actual volume used, compared between hemielipsoid-guided and historical surgeon estimation	Intraoperative (Day 1)

Collaborators and Investigators

• Sponsor: Sakarya University

Study record dates

Study Major Dates

• Study Start (Actual): June 1, 2026
• Primary Completion (Estimated): June 1, 2027
• Study Completion (Estimated): July 1, 2027

Study Registration Dates

• First Submitted: June 11, 2026
• First Submitted That Met QC Criteria: June 11, 2026
• First Posted (Actual): June 17, 2026

Study Record Updates

• Last Update Posted (Actual): June 17, 2026
• Last Update Submitted That Met QC Criteria: June 11, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Keywords: hemielipsoid formula, bone defect volume, allograft planning, orthopedic oncology, fluid displacement
• Additional Relevant MeSH Terms: Bone Diseases; Musculoskeletal Diseases; Neoplasms by Site; Neoplasms; Bone Neoplasms
• Other Study ID Numbers: E-43012747-050.04-543070-646

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual participant data will not be shared publicly due to patient privacy considerations and institutional policy.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No